Bump actions/checkout from 4 to 5 in /.github/util/initialize (#2621)

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 5.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...v5)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '5'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/util/initialize/action.yml

@@ -45,7 +45,7 @@ runs:
     # downloading repo via GitHub API.
     - name: Check out the language repo
       if: github.event_name != 'pull_request'
-      uses: actions/checkout@v4
+      uses: actions/checkout@v5
       with: {repository: sass/sass, path: build/language}
 
     - name: Generate Dart from protobuf