Bump actions/checkout from 3 to 4

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]>

.github/workflows/combine-prs.yml

@@ -95,7 +95,7 @@ jobs:
             console.log('Combined: ' + combined);
             return combined
       # Checks-out your repository under $GITHUB_WORKSPACE, so your job can access it
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
         with:
           fetch-depth: 0
       # Creates a branch with other PR branches merged together

.github/workflows/gradle-wrapper-validation.yml

@@ -17,5 +17,5 @@ jobs:
       run:
         working-directory: jsonschema2pojo-gradle-plugin/example/android
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - uses: gradle/wrapper-validation-action@v1