ci: do not login to docker registry in PRs

Signed-off-by: Mark Sagi-Kazar <mark.sagikazar@gmail.com>

.github/workflows/ci.yml

@@ -122,6 +122,7 @@ jobs:
         with:
           username: ${{ secrets.DOCKER_USERNAME }}
           password: ${{ secrets.DOCKER_PASSWORD }}
+        if: github.event_name == 'push'
 
       - name: Build and Push
         uses: docker/build-push-action@v2