Bump actions/checkout from 3 to 4 (#51)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v3...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  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>

.github/workflows/gradle.yml

@@ -19,7 +19,7 @@ jobs:
         password: ${{ secrets.DOCKER_HUB_TOKEN }}
 
     - name: checkout repo
-      uses: actions/checkout@v3
+      uses: actions/checkout@v4
 
     - name: set up JDK
       uses: actions/setup-java@v3