fix(ci): mkdir -p /var/lib/dbus before writing machine-id

The flatpak-github-actions container does not have /var/lib/dbus,
causing tee to fail with 'No such file or directory'. Create the
directory before writing the machine-id.

Assisted-by: Claude Sonnet 4.6 via OpenCode

Author: castrojo

.github/workflows/build.yml

@@ -1057,7 +1057,7 @@ jobs:
       - name: Ensure machine-id exists
         if: steps.arch-check.outputs.skip != 'true'
         run: |
-          dbus-uuidgen | tee /var/lib/dbus/machine-id
+          mkdir -p /var/lib/dbus && dbus-uuidgen | tee /var/lib/dbus/machine-id
 
       - name: Install ${{ matrix.app }}
         if: steps.arch-check.outputs.skip != 'true'