mkosi: Update to latest

mkosi now installs a "ignore *" default preset on Debian. We also
switch Debian to dbus-broker now that preset doesn't disable it
anymore.

.github/workflows/mkosi.yml

@@ -73,7 +73,7 @@ jobs:
 
     steps:
     - uses: actions/checkout@ac593985615ec2ede58e132d2e21d2b1cbd6127c
-    - uses: systemd/mkosi@779484101987048b820b07a6111bcb0e8d5ebc1d
+    - uses: systemd/mkosi@268a9374d5a93a4021db6521a39db2c2ed9fd755
 
     - name: Configure
       run: |