Only log in to DockerHub on `push` event

.github/workflows/ci.yml

@@ -25,6 +25,7 @@ jobs:
         uses: docker/setup-buildx-action@v1
 
       - name: Login to DockerHub
+        if: github.event_name == 'push'
         uses: docker/login-action@v1
         with:
           username: ${{ secrets.DOCKERHUB_USERNAME }}