ci: allow a label to trigger multiarch CI

Author: nbdd0121

.github/workflows/ci.yml

@@ -46,7 +46,7 @@ jobs:
           echo '| Package | System | Status |' >> $GITHUB_STEP_SUMMARY
           echo '|---------|--------|--------|' >> $GITHUB_STEP_SUMMARY
 
-          if ${{ github.event_name == 'pull_request' }}; then
+          if ${{ github.event_name == 'pull_request' && !contains(github.event.pull_request.labels.*.name, 'CI:Multiarch') }}; then
             # We only support MacOS with best-effort basis. They take much longer to build so shouldn't block PR.
             SYSTEMS=(x86_64-linux)
           else