bug#42720: 28.0.50; mml-first-secure-en-decrypt-sign-1 test failing on Fedora 31

[Paul Eggert <eggert@cs.ucla.edu>]

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Even with yesterday's patch to test/lisp/gnus/mml-sec-tests.el, Emacs master 
'make check' is currently failing the mml-first-secure-en-decrypt-sign-1 test on 
Fedora 31 x86-64. I'm attaching a failed test log.

Here are details about the configuration.

In GNU Emacs 28.0.50 (build 6, x86_64-pc-linux-gnu, GTK+ Version 3.24.13, cairo 
version 1.16.0)
  of 2020-08-05 built on Penguin.CS.UCLA.EDU
Repository revision: b22b1f935d47c71b59d59da1b6d125635470beca
Repository branch: master
System Description: Fedora 31 (Workstation Edition)

Recent messages:

Configured using:
  'configure --enable-gcc-warnings'

Configured features:
XPM JPEG TIFF GIF PNG RSVG CAIRO SOUND GPM DBUS GSETTINGS GLIB NOTIFY
INOTIFY ACL LIBSELINUX GNUTLS LIBXML2 FREETYPE HARFBUZZ M17N_FLT LIBOTF
ZLIB TOOLKIT_SCROLL_BARS GTK3 X11 XDBE XIM MODULES THREADS LIBSYSTEMD
JSON PDUMPER LCMS2

Important settings:
   value of $LC_ALL: en_US.utf8
   value of $LC_COLLATE: en_US.UTF-8
   value of $LC_CTYPE: en_US.UTF-8
   value of $LC_MESSAGES: en_US.UTF-8
   value of $LANG: C
   locale-coding-system: utf-8-unix

Major mode: Lisp Interaction

Minor modes in effect:
   global-whitespace-mode: t
   tooltip-mode: t
   global-eldoc-mode: t
   eldoc-mode: t
   electric-quote-mode: t
   electric-indent-mode: t
   mouse-wheel-mode: t
   tool-bar-mode: t
   menu-bar-mode: t
   file-name-shadow-mode: t
   global-font-lock-mode: t
   font-lock-mode: t
   auto-composition-mode: t
   auto-encryption-mode: t
   auto-compression-mode: t
   line-number-mode: t
   transient-mark-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message rmc puny dired dired-loaddefs
rfc822 mml mml-sec epa derived epg epg-config gnus-util rmail
rmail-loaddefs text-property-search time-date mm-decode mm-bodies
mm-encode mail-parse rfc2231 mailabbrev gmm-utils mailheader sendmail
rfc2047 rfc2045 ietf-drums mm-util mail-prsvr mail-utils term/xterm
xterm whitespace package easymenu browse-url url-handlers url-parse
auth-source cl-seq eieio eieio-core cl-macs eieio-loaddefs
password-cache json subr-x map url-vars seq byte-opt gv bytecomp
byte-compile cconv cl-loaddefs cl-lib tooltip eldoc electric uniquify
ediff-hook vc-hooks lisp-float-type mwheel term/x-win x-win
term/common-win x-dnd tool-bar dnd fontset image regexp-opt fringe
tabulated-list replace newcomment text-mode elisp-mode lisp-mode
prog-mode register page tab-bar menu-bar rfn-eshadow isearch timer
select scroll-bar mouse jit-lock font-lock syntax facemenu font-core
term/tty-colors frame minibuffer cl-generic cham georgian utf-8-lang
misc-lang vietnamese tibetan thai tai-viet lao korean japanese eucjp-ms
cp51932 hebrew greek romanian slovak czech european ethiopic indian
cyrillic chinese composite charscript charprop case-table epa-hook
jka-cmpr-hook help simple abbrev obarray cl-preloaded nadvice loaddefs
button faces cus-face macroexp files text-properties overlay sha1 md5
base64 format env code-pages mule custom widget hashtable-print-readable
backquote threads dbusbind inotify lcms2 dynamic-setting
system-font-setting font-render-setting cairo move-toolbar gtk x-toolkit
x multi-tty make-network-process emacs)

Memory information:
((conses 16 648701 9307)
  (symbols 48 7636 2)
  (strings 32 20659 1692)
  (string-bytes 1 689813)
  (vectors 16 10653)
  (vector-slots 8 109771 9795)
  (floats 8 25 269)
  (intervals 56 205 0)
  (buffers 992 10))

[-- Attachment #2: mml-sec-tests.log --]
[-- Type: text/x-log, Size: 2724 bytes --]

Running 20 tests (2020-08-05 08:05:47-0700, selector `(not (or (tag :expensive-test) (tag :unstable)))')
Test mml-first-secure-en-decrypt-sign-1 backtrace:
  signal(epg-error ("Encrypt failed" "Exit"))
  mml-secure-test-fixture(#f(compiled-function () #<bytecode 0x6ccefb2
  mml-secure-test-key-fixture(#f(compiled-function () #<bytecode -0x77
  #f(compiled-function () #<bytecode -0xc26ac755dcd02aa>)()
  ert--run-test-internal(#s(ert--test-execution-info :test #s(ert-test
  ert-run-test(#s(ert-test :name mml-first-secure-en-decrypt-sign-1 :d
  ert-run-or-rerun-test(#s(ert--stats :selector (not ...) :tests [... 
  ert-run-tests((not (or (tag :expensive-test) (tag :unstable))) #f(co
  ert-run-tests-batch((not (or (tag :expensive-test) (tag :unstable)))
  ert-run-tests-batch-and-exit((not (or (tag :expensive-test) (tag :un
  eval((ert-run-tests-batch-and-exit '(not (or (tag :expensive-test) (
  command-line-1(("-L" ":." "-l" "ert" "-l" "lisp/gnus/mml-sec-tests" 
  command-line()
  normal-top-level()
Test mml-first-secure-en-decrypt-sign-1 condition:
    (epg-error "Encrypt failed" "Exit")
   FAILED   1/20  mml-first-secure-en-decrypt-sign-1 (0.673274 sec)
   passed   2/20  mml-secure-en-decrypt-1 (0.454633 sec)
   passed   3/20  mml-secure-en-decrypt-2 (0.472967 sec)
   passed   4/20  mml-secure-en-decrypt-3 (0.511085 sec)
   passed   5/20  mml-secure-en-decrypt-4 (0.496392 sec)
  skipped   6/20  mml-secure-en-decrypt-passphrase-cache (0.000148 sec)
  skipped   7/20  mml-secure-en-decrypt-passphrase-no-cache-openpgp-todo (0.003517 sec)
   failed   8/20  mml-secure-en-decrypt-passphrase-no-cache-smime-todo (0.000149 sec)
   passed   9/20  mml-secure-en-decrypt-sign-2 (1.770544 sec)
   passed  10/20  mml-secure-en-decrypt-sign-3 (0.599651 sec)
   passed  11/20  mml-secure-find-usable-keys-1 (0.088486 sec)
   passed  12/20  mml-secure-find-usable-keys-2 (0.099421 sec)
   passed  13/20  mml-secure-key-checks (0.143075 sec)
   passed  14/20  mml-secure-select-preferred-keys-1 (0.006005 sec)
   passed  15/20  mml-secure-select-preferred-keys-2 (0.036085 sec)
   passed  16/20  mml-secure-select-preferred-keys-3 (0.016259 sec)
   passed  17/20  mml-secure-select-preferred-keys-4 (0.042690 sec)
   passed  18/20  mml-secure-sign-verify-1 (1.206041 sec)
   passed  19/20  mml-secure-sign-verify-2 (1.485268 sec)
   passed  20/20  mml-secure-sign-verify-3 (0.020467 sec)

Ran 20 tests, 17 results as expected, 1 unexpected, 2 skipped (2020-08-05 08:05:56-0700, 8.330873 sec)
1 expected failures

1 unexpected results:
   FAILED  mml-first-secure-en-decrypt-sign-1

2 skipped results:
  SKIPPED  mml-secure-en-decrypt-passphrase-cache
  SKIPPED  mml-secure-en-decrypt-passphrase-no-cache-openpgp-todo