ci: disable scheduled build/push on forks

See nginx-proxy/nginx-proxy#2586

Author: buchdag

.github/workflows/build-publish.yml

@@ -22,6 +22,7 @@ jobs:
   multiarch-build:
     name: Build and publish Docker image
     runs-on: ubuntu-latest
+    if: (github.event_name == "schedule" && github.repository == "nginx-proxy/acme-companion") || (github.event_name != "schedule")
     steps:
       - name: Checkout
         uses: actions/checkout@v4