ci: test docker build only on master

Author: ReaJason

.github/workflows/test.yaml

@@ -40,6 +40,7 @@ jobs:
 
   docker-build-test:
     runs-on: ubuntu-latest
+    if: github.ref == 'refs/heads/master'
     steps:
       - name: Checkout code
         uses: actions/checkout@v4