mkosi: update debian commit reference

* 4447d2974d Update changelog for 257.2-3 release
* 4b1c65b905 libudev1: add udeb back to shlibs
* 1974e3d06e systemd-boot: always check that the boot entry is set, even with Shim is already installed
* 9a5eea9823 systemd-boot: use boot entry argument instead of installing as grub.efi on ESP
* df6efeed46 libsystemd-dev/libudev-dev: depend on libcap-dev
* 5673b771e1 signing template: add override for executable-not-elf-or-script
* 3f109637c4 Update changelog for 257.2-2 release
* 42f4afa605 Drop udeb packages
* c04f7f2b16 signing template: always set urgency to 'high'
* 9bd8b5228b Set SBAT info for upstream build
* 257ba8563b udev: link to libsystemd-shared when building with noudeb profile
* 8ca2b26678 Link systemctl against libsystemd-shared
* 1a4a8af0c2 Install jq for pkg.systemd.upstream too since the template packages are now built
* 6fd0d2698d signing template: fix Lintian warnings and errors
* c79d10bbaa Build template packages for pkg.systemd.upstream profile, for OBS builds
* 485a867438 d/t/upstream: take into account autopkgtest pinning
* c1b6e565e3 Update README.source in the signing-template
* 17d1b92d9f d/t/control: remove 'flaky' from tests-in-lxd
* 2a36f6f5e1 Do not install sd-resolved and drop breaks-testbed from fast tests
* a3cb52f8d0 Enable UEFI on loong64
* ad7a943023 Enable libseccomp on loong64 and hppa
* 9d24f84ed5 Update changelog for 257.2-1 release
* f47619c9f4 Drop all patches, merged upstream
* d4aa6545a6 Install new files for upstream CI
* 5775daa46e d/rules: support building in OBS from git

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=7dc7ee80070e38b1c603104455c0077b6879e1fe
+        GIT_COMMIT=4447d2974d16992c2dc88bb451d2be7dd1d7192f
         PKG_SUBDIR=debian
 
 [Content]