chore: release v6.0.0 for Node.js 24 support

- Update to Node.js 24 runtime (runs.using: node24)
- Bump version to 6.0.0
- Update README with v6 release notes
- Rebuild dist

package.json

@@ -1,6 +1,6 @@
 {
   "name": "upload-artifact",
-  "version": "5.0.0",
+  "version": "6.0.0",
   "description": "Upload an Actions Artifact in a workflow run",
   "main": "dist/upload/index.js",
   "scripts": {