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/check-dist.yml

@@ -22,7 +22,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v4.1.6
+      - uses: actions/checkout@v6
 
       - name: Set Node.js 24.x
         uses: actions/setup-node@v4