ci: Fix install-common-dependencies.sh -h

The option is advertised as alternative to --help, but doesn't
actually work. While not super important for a script that isn't
user facing, it's a trivial fix and doesn't hurt.

Part-of: <https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4074>

.gitlab-ci/install-common-dependencies.sh

@@ -19,7 +19,7 @@ usage() {
 
 TEMP=$(getopt \
   --name=$(basename $0) \
-  --options='' \
+  --options='h' \
   --longoptions='libdir:' \
   --longoptions='destdir:' \
   --longoptions='help' \