bug#54663: 29.0.50; align-current changed behavior

[Henri Menke via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

Somewhere between version 27.1 and 29.0.50 the `align' command changed
its behavior. Examples below are executed in emacs -Q.

Consider the following file `test.tex':

   \documentclass{article}
   \begin{document}
   \begin{tabular}{lr}
     abc def & zzz \\
     foo & bar \\
   \end{tabular}
   \end{document}

Opening this file in 27.1 and using M-x align-current yields the
expected

   \documentclass{article}
   \begin{document}
   \begin{tabular}{lr}
     abc def & zzz \\
     foo     & bar \\
   \end{tabular}
   \end{document}

but opening the file in 29.0.50 and using M-x align-current produces
something weird:

   \documentclass{article}
   \begin{document}
   \begin{tabular}{lr}
    abc def   & zzz \\
    foo & bar \\
   \end{tabular}
   \end{document}

There is only a single space of indentation and alignment is now at
spaces instead of & and \\ as expected for align-tex-modes.

;;===================
In GNU Emacs 29.0.50 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.30, cairo version 1.16.0)
Repository revision: 6f973faa912a5ac1ba643c6f5deb0c02baa0ba6d
Repository branch: master
System Description: NixOS 21.11 (Porcupine)

Configured using:
 'configure
 --prefix=/nix/store/b65vgqd1kdfxaly3y3yn3f3qkcrbdkwq-emacs-pgtkgcc-20220330.0
 --disable-build-details --with-modules --with-x-toolkit=gtk3
 --with-cairo --with-native-compilation --with-pgtk'

Configured features:
CAIRO DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON
LIBOTF LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY
PDUMPER PGTK PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF
TOOLKIT_SCROLL_BARS XIM GTK3 ZLIB

Important settings:
  value of $LANG: en_US.UTF-8
  locale-coding-system: utf-8-unix

Major mode: LaTeX

Minor modes in effect:
  shell-dirtrack-mode: t
  tooltip-mode: t
  global-eldoc-mode: t
  show-paren-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
  blink-cursor-mode: t
  line-number-mode: t
  transient-mark-mode: t
  auto-composition-mode: t
  auto-encryption-mode: t
  auto-compression-mode: t

Load-path shadows:
None found.

Features:
(shadow sort mail-extr emacsbug message mailcap yank-media rmc puny
dired dired-loaddefs rfc822 mml mml-sec password-cache epa derived epg
rfc6068 epg-config gnus-util seq gv byte-opt bytecomp byte-compile cconv
mm-decode mm-bodies mm-encode mail-parse rfc2231 mailabbrev gmm-utils
mailheader sendmail rfc2047 rfc2045 ietf-drums mm-util mail-prsvr
mail-utils misearch multi-isearch time-date subr-x align vc-git
diff-mode easy-mmode vc-dispatcher cl-loaddefs cl-lib tex-mode compile
text-property-search shell pcomplete comint ansi-color ring latexenc
iso-transl tooltip eldoc paren electric uniquify ediff-hook vc-hooks
lisp-float-type elisp-mode mwheel term/pgtk-win pgtk-win term/common-win
tool-bar dnd fontset image regexp-opt fringe tabulated-list replace
newcomment text-mode lisp-mode prog-mode register page tab-bar menu-bar
rfn-eshadow isearch easymenu timer select scroll-bar mouse jit-lock
font-lock syntax font-core term/tty-colors frame minibuffer nadvice
simple 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
emoji-zwj charscript charprop case-table epa-hook jka-cmpr-hook help
abbrev obarray oclosure cl-preloaded button loaddefs faces cus-face
macroexp files window text-properties overlay sha1 md5 base64 format env
code-pages mule custom widget keymap hashtable-print-readable backquote
threads dbusbind inotify dynamic-setting system-font-setting
font-render-setting cairo gtk pgtk multi-tty make-network-process
native-compile emacs)

Memory information:
((conses 16 85785 5008)
 (symbols 48 7342 0)
 (strings 32 23176 1221)
 (string-bytes 1 811910)
 (vectors 16 16616)
 (vector-slots 8 331153 7610)
 (floats 8 35 312)
 (intervals 56 866 0)
 (buffers 992 11))