Fixes an issue with github action in job build-spark-operator

[aneagoe]

It seems that https://github.com/GoogleCloudPlatform/spark-on-k8s-operator/pull/1418/files introduces a bug in the workflow, at step Check changes in resources used in docker file in job build-spark-operator:

      - name: Check changes in resources used in docker file
        run: |
          DOCKERFILE_RESOURCES=$(cat Dockerfile | grep -P -o "COPY [a-zA-Z0-9].*? " | cut -c6-)
          for resource in $DOCKERFILE_RESOURCES; do
            # If the resource is different
            if ! git diff  --quiet origin/master -- $resource; then
              ## And the appVersion hasn't been updated
              if ! git diff --quiet charts/spark-operator-chart/Chart.yaml | grep +appVersion; then
                echo "resource used in gcr.io/spark-operator/spark-operator has changed in $resource, need to update the appVersion in charts/spark-operator-chart/Chart.yaml"
                git diff origin/master -- $resource;
                echo "failing the build... " && false
              fi
            fi
          done

Basically, git diff --quiet charts/spark-operator-chart/Chart.yaml | grep +appVersion would always fail since --quiet removes all output and can't be used together with grep. As a consequence, the required changes to Chart.yaml are never detected and builds would fail.