bug#67567: 30.0.50; mode-line-inactive face no longer light gray

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

Somewhere within the past several commits the inactive mode line face
ceased being assigned a background color distinct from the that of
mode-line.  This problem manifests itself in emacs -Q as well, and
should be a recent phenomenon, but I am presently short on time to
further investigate or correct it.

TIA.

In GNU Emacs 30.0.50 (build 1, x86_64-pc-linux-gnu) of 2023-12-01 built
 on trinity
Repository revision: 90450a387422f025b7060a3a7977f30ae395bb1d
Repository branch: HEAD
Windowing system distributor 'The X.Org Foundation', version 11.0.12014000
System Description: Fedora Linux 39 (Workstation Edition)

Configured using:
 'configure --with-x-toolkit=no --without-cairo
 --with-native-compilation=aot --cache-file=/tmp/ccache'

Configured features:
ACL DBUS FREETYPE GIF GLIB GMP GNUTLS GSETTINGS HARFBUZZ JPEG JSON LCMS2
LIBSELINUX LIBSYSTEMD LIBXML2 MODULES NATIVE_COMP NOTIFY INOTIFY
OLDXMENU PDUMPER PNG RSVG SECCOMP SOUND SQLITE3 THREADS TIFF TREE_SITTER
WEBP X11 XDBE XFT XIM XINPUT2 XPM ZLIB

Important settings:
  value of $LC_MONETARY: en_US.UTF-8
  value of $LC_NUMERIC: en_US.UTF-8
  value of $LC_TIME: en_US.UTF-8
  value of $LANG: en_US.utf8
  value of $XMODIFIERS: @im=none
  locale-coding-system: utf-8-unix

Major mode: Article