move IMAGE_BASENAME to global variables

.gitlab-ci.yml

@@ -3,6 +3,9 @@ include:
   ref: master
   file: docker_hub.gitlab-ci.yml
 
+variables:
+  IMAGE_BASENAME: ${IMAGE_PREFIX}/flutter
+
 .build_flutter_base:
   variables:
     BUILD_ARGS: FLUTTER_VERSION=${VERSION}
@@ -12,6 +15,5 @@ include:
   - .build_flutter_base
   - .build_image_job_template
   variables:
-    IMAGE_BASENAME: ${IMAGE_PREFIX}/flutter
     VERSION: 3.24.5
     IMAGE_NAME: ${IMAGE_BASENAME}:${VERSION},${IMAGE_BASENAME}:3.24,${IMAGE_BASENAME}:3