Update CI to Node v21

Author: meronz

.github/workflows/publish.yml

@@ -10,7 +10,7 @@ jobs:
       - uses: actions/checkout@v2
       - uses: actions/setup-node@v1
         with:
-          node-version: 12
+          node-version: 21
       - run: npm ci
       - name: Publish to Open VSX Registry
         uses: HaaLeo/publish-vscode-extension@v0