Add helper for case-independent string equality checks

(cherry picked from commit bd47b0dac4a1ff6e686c99b9958693e86d44007b)

Gbp-Pq: Name Add-helper-for-case-independent-string-equality-checks.patch

systemd (247.3-7+deb11u7) bullseye-security; urgency=medium

  * Non-maintainer upload by the LTS Team.
  * debian/patches/:
    - CVE-2025-4598-{0,1,2,3,4}.patch: import and backport patches
      from upstream to fix CVE-2025-4598.
    - fix-stack-overflow-in-coredump-filter-{0,1,2}.patch: import and
      backport patches from upstream to fix CoredumpFilter=all overflow.
  * debian/salsa-ci.yml: add (E)LTS pipeline for bullseye.

[dgit import unpatched systemd 247.3-7+deb11u7]

Import systemd_247.3-7+deb11u7.debian.tar.xz

[dgit import tarball systemd 247.3-7+deb11u7 systemd_247.3-7+deb11u7.debian.tar.xz]

Import systemd_247.3.orig.tar.gz

[dgit import orig systemd_247.3.orig.tar.gz]