Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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] <[email protected]>

Author: dependabot[bot]

.github/workflows/ci-main.yml

@@ -29,7 +29,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
       - name: Log in to GitHub Container Registry
         uses: docker/login-action@v2
         with:

.github/workflows/release.yml

@@ -38,7 +38,7 @@ jobs:
       contents: read
       packages: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           ref: ${{ needs.CI.outputs.version }}
       - name: Log in to GitHub Container Registry