mkosi: update debian commit reference

* 7eebe8c0b1 autopkgtest: allow localectl in localed tests
* c08a88ffbb Update changelog for 256.4-1 release
* 03814c87fe Fix D-Bus policy for locale1 blocking
* 16f6130038 Drop last patch, all merged upstream
* fe6956e934 Install varlinkctl zsh completion file
* 9bc2a52832 Update upstream source from tag 'upstream/256.4'
* 8574241978 New upstream version 256.4

mkosi.images/build/mkosi.conf.d/debian-ubuntu/mkosi.conf

@@ -9,7 +9,7 @@ Environment=
         GIT_URL=https://salsa.debian.org/systemd-team/systemd.git
         GIT_SUBDIR=debian
         GIT_BRANCH=debian/master
-        GIT_COMMIT=c7138e0b872ed474ae5568f7995b9f7a0c5c3679
+        GIT_COMMIT=7eebe8c0b1805c9f8ec86be8167ee41fa2a232a4
         PKG_SUBDIR=debian
 
 Packages=