ci: Only build custom images that need to be rebuilt

Signed-off-by: Rémy Coutable <remy@rymai.me>

.gitlab/ci/gitlab.images.yml

@@ -1,7 +1,17 @@
 # Used by GitLab: https://gitlab.com/gitlab-org/gitlab/blob/master/.gitlab-ci.yml
+.gitlab:
+  extends:
+    - .build_dynamic_image
+  stage: gitlab
+  rules:
+    - !reference [.build_dynamic_image, rules]
+    - changes:
+        - "scripts/lib/custom-docker-build"
+        - ".gitlab/ci/gitlab.images.yml"
+
 gitlab:
   extends:
-    - .build_and_push
+    - .gitlab
   stage: gitlab
   variables:
     RUBYGEMS: '3.2'
@@ -22,8 +32,7 @@ gitlab:
 
 gitlab-ruby-3.2:
   extends:
-    - .build_and_push
-  stage: gitlab
+    - .gitlab
   variables:
     RUBYGEMS: '3.4'
     LFS: '2.9'
@@ -44,7 +53,7 @@ gitlab-ruby-3.2:
 # Used by GitLab's compile-production-assets and compile-test-assets jobs
 gitlab-assets:
   extends:
-    - .build_and_push
+    - .gitlab
   stage: gitlab-assets
   variables:
     RUBYGEMS: '3.2'
@@ -62,7 +71,7 @@ gitlab-assets:
 # Used by GitLab's Review app jobs
 gitlab-review-app:
   extends:
-    - .build_and_push
+    - .gitlab
   stage: gitlab-review-app
   variables:
     RUBY: '3.0'