Add resource_group for build jobs

shared-ci.yml

@@ -46,6 +46,10 @@ image: registry.git.cccv.de/infra/packages/docker-images/utility
     when: manual
   - if: '$RUN_AUTOUPDATE != "1"'
   stage: build
+  # Ensure that build jobs only run one at a time to prevent excessive
+  # resource usage when many releases are added at the same time
+  # (e.g. security updates for multiple versions)
+  resource_group: build
   dependencies: []
   needs: []