Bump actions/checkout from 5 to 6 (#1559)

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
...

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

.github/workflows/docker.yml

@@ -42,7 +42,7 @@ jobs:
           echo "tag=gpsbabel_$(echo ${{ inputs.version }} | tr . _)" >> "$GITHUB_OUTPUT"
         fi
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
       with:
         ref: ${{ steps.compute.outputs.tag }}
         fetch-depth: 0