Bump actions/checkout from 2.3.4 to 2.4.0

Bumps [actions/checkout](https://github.com/actions/checkout) from 2.3.4 to 2.4.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](https://github.com/actions/checkout/compare/v2.3.4...v2.4.0)

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

Signed-off-by: dependabot[bot] <support@github.com>

.github/workflows/milestone-management.yml

@@ -14,7 +14,7 @@ jobs:
   new_milestone:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v2.3.4
+      - uses: actions/checkout@v2.4.0
       - uses: ./.github/actions/milestone-management
         with:
           repo-token: ${{ secrets.GITHUB_TOKEN }}