Added image ref for scanning

Author: LondheShubham153

.github/workflows/image-scan.yml

@@ -18,6 +18,7 @@ jobs:
             - name: Trivy Scanner
               uses: aquasecurity/trivy-action@0.33.1
               with:
+                image-ref: ${{ vars.DOCKERHUB_USER }}/github-actions-app:${{ github.sha}}
                 severity: 'CRITICAL'
                 exit-code: '1'