[2.x] ci: bump actions/checkout from 6 to 7 (#9366)

Bumps [actions/checkout](https://github.com/actions/checkout) from 6 to 7.
- [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/v6...v7)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '7'
  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/server-test.yml

@@ -14,7 +14,7 @@ jobs:
       JVM_OPTS: -Xms800M -Xmx2G -Xss6M -XX:ReservedCodeCacheSize=128M -server -Dsbt.io.virtual=false -Dfile.encoding=UTF-8
       SBT_ETC_FILE: $HOME/etc/sbt/sbtopts
     steps:
-    - uses: actions/checkout@v6
+    - uses: actions/checkout@v7
     - name: Setup JDK
       uses: actions/setup-java@v5
       with: