[CI] Enclose double stars

.gitlab-ci.yml

@@ -60,8 +60,8 @@ set-variables:
   # Otherwise, may be triggered manually.
   rules:
     - changes:
-      - **/Dockerfile
-      - **/docker-compose.yml
+      - "**/Dockerfile"
+      - "**/docker-compose.yml"
       when: always
     - when: manual
   only:
@@ -86,7 +86,7 @@ build:
   # Otherwise, may be triggered manually.
   rules:
     - changes:
-      - **/Dockerfile
+      - "**/Dockerfile"
       when: always
     - when: manual
   only: