ci: use Github environment files

- fixing vulnerability via https://docs.github.com/en/free-pro-team@latest/actions/reference/workflow-commands-for-github-actions#environment-files

.github/workflows/vulnscan.yml

@@ -17,7 +17,7 @@ jobs:
     - name: Install Trivy
       run: |
         mkdir -p $GITHUB_WORKSPACE/bin
-        echo "::add-path::$GITHUB_WORKSPACE/bin"
+        echo "$GITHUB_WORKSPACE/bin" >> "$GITHUB_PATH"
         curl -sfL https://raw.githubusercontent.com/aquasecurity/trivy/master/contrib/install.sh | sh -s -- -b $GITHUB_WORKSPACE/bin
     - name: Download Trivy DB
       run: |