fix: update Node.js version to 20 in release workflow and reduce Discord spam

- Update release workflow Node.js version from 18 to 20 to match package.json requirements
- Remove push trigger from Discord workflow to reduce notification spam

This should resolve the semantic-release content-length header error after org migration.

.github/workflows/release.yaml

@@ -32,7 +32,7 @@ jobs:
       - name: Setup Node.js
         uses: actions/setup-node@v4
         with:
-          node-version: '18'
+          node-version: '20'
           cache: npm
           registry-url: https://registry.npmjs.org
       - name: Install dependencies