Add condition to skip Trivy vulnerability scanner on pull requests

.github/workflows/docker-image.yml

@@ -61,6 +61,7 @@ jobs:
  cache-from: type=gha
  cache-to: type=gha,mode=max
  - name: Run Trivy vulnerability scanner
+ if: ${{ github.event_name != 'pull_request' }}
  uses: aquasecurity/trivy-action@master
  with:
  image-ref: ${{ fromJSON(steps.build-and-push.outputs.metadata)['image.name'] }}