ci: Use dry-run install during the build test

We already test install as part of other jobs (such as
can-build-gnome-shell) and in general that's wrong because we may
add to the final install path artifacts that are required during tests,
hiding potential issues with meson test when those files are not
installed.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/3016>

.gitlab-ci.yml

@@ -241,7 +241,7 @@ check-code-style:
         $BASE_MESON_OPTIONS
         $EXTRA_MESON_OPTIONS
     - meson compile -C build
-    - meson install -C build
+    - meson install --dry-run -C build
   artifacts:
     expire_in: 1 day
     paths: