ci: only release docker on scheduled builds.

Author: jrfaller

.github/workflows/build-test-gumtree.yml

@@ -78,7 +78,8 @@ jobs:
   docker:
     runs-on: ubuntu-latest
     needs: build-test-deploy
-    if: ${{ !(contains(github.event.head_commit.message, '[no ci]') || startsWith(github.event.head_commit.message, 'doc')) }}
+
+    if: ${{ github.event_name == 'schedule' && !(contains(github.event.head_commit.message, '[no ci]') || startsWith(github.event.head_commit.message, 'doc')) }}
     steps:
       - name: set up docker buildx
         uses: docker/setup-buildx-action@v3