chore(deps): update docker.io/gitlab/gitlab-ce docker tag to v18.8.4

library/compose/gitlab/compose.yaml.j2

@@ -1,6 +1,6 @@
 services:
   {{ service_name }}:
-    image: docker.io/gitlab/gitlab-ce:18.8.3-ce.0
+    image: docker.io/gitlab/gitlab-ce:18.8.4-ce.0
     restart: {{ restart_policy }}
     shm_size: '256m'
     env_file: .env