ci: Don't run docker builds on foreign MRs

.gitlab-ci.yml

@@ -473,7 +473,8 @@ docker:
           --set *.cache-to=type=registry,ref=$DOCKER_CACHE_IMAGE:$CI_COMMIT_BRANCH,mode=max,oci-mediatypes=false
           --push
 
-    - if: $CI_PIPELINE_SOURCE == "merge_request_event"
+    - if: $CI_PIPELINE_SOURCE == "merge_request_event" && $CI_PROJECT_NAME == "funkwhale"
+      # We don't provide priviledged runners to everyone, so we can only build docker images in the funkwhale group
       variables:
         BUILD_ARGS: >
           --set *.platform=linux/amd64