CI: build on PRs, push only from master

Author: ohmyfelix

.github/workflows/docker.yml

@@ -3,8 +3,9 @@ name: "Docker"
 on:
   workflow_dispatch:
 
+  pull_request:
+
   push:
-    branches: ["master"]
 
   schedule:
     - cron: "0 8 * * 1"
@@ -74,7 +75,7 @@ jobs:
         uses: docker/setup-buildx-action@v3
 
       - name: Login to DockerHub
-        if: github.ref == 'refs/heads/master'
+        if: github.event_name == 'push' && github.ref == 'refs/heads/master'
         uses: docker/login-action@v3
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}
@@ -104,7 +105,7 @@ jobs:
           docker stop $CONTAINER_ID
 
       - name: Build and push to registry
-        if: github.ref == 'refs/heads/master'
+        if: github.event_name == 'push' && github.ref == 'refs/heads/master'
         uses: docker/build-push-action@v6
         with:
           context: ${{ matrix.context }}