build(deps): bump actions/checkout from 5 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 5 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v5...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: '6'
  dependency-type: direct:production
  update-type: version-update:semver-major
...

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

Author: dependabot[bot]

.github/workflows/ci.yaml

@@ -21,6 +21,6 @@ jobs:
       with:
         go-version: ${{ matrix.go-version }}
     - name: Checkout code
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Run tests
       run: go test -v -covermode=count ./...