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](https://github.com/actions/checkout/compare/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] <support@github.com>

.github/workflows/claude.yml

@@ -54,7 +54,7 @@ jobs:
 
       - name: Checkout PR branch
         if: steps.pr.outcome == 'success'
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           ref: ${{ steps.pr.outputs.sha }}
           repository: ${{ steps.pr.outputs.repo }}
@@ -62,7 +62,7 @@ jobs:
 
       - name: Checkout repository
         if: steps.pr.outcome != 'success'
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           fetch-depth: 0