Update all references from v5 and v4 to v6 (#2314)

- Updated README.md examples to reference @v6
- Updated all workflow files to use actions/checkout@v6

.github/workflows/licensed.yml

@@ -9,6 +9,6 @@ jobs:
     runs-on: ubuntu-latest
     name: Check licenses
     steps:
-      - uses: actions/checkout@v4.1.6
+      - uses: actions/checkout@v6
       - run: npm ci
       - run: npm run licensed-check