ci: Launch pipewire through the meta-dbus-runner

We can just launch pipewire first and then wireplumber so that the test
script can be simplified

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3793>

.gitlab-ci.yml

@@ -484,7 +484,6 @@ build-wayland-only@x86_64:
     - !reference [.mutter.git-clone, before_script]
     # Disable e.g. audio support to not dead lock screen cast tests
     - mkdir -m 700 $XDG_RUNTIME_DIR
-    - pipewire & sleep 2
 
 .test-mutter-base:
   extends:
@@ -517,6 +516,7 @@ build-wayland-only@x86_64:
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
     - xvfb-run -a -s "$XVFB_SERVER_ARGS"
         ./src/tests/meta-dbus-runner.py
+          --launch=pipewire
           --launch=wireplumber
           meson test
             -C build
@@ -678,6 +678,7 @@ dist-mutter:
     - glib-compile-schemas $GSETTINGS_SCHEMA_DIR
     - xvfb-run -a -s "$XVFB_SERVER_ARGS"
         ./src/tests/meta-dbus-runner.py
+          --launch=pipewire
           --launch=wireplumber
           meson dist -C build
   artifacts: