Bump actions/checkout from 5 to 6 in /.github/workflows

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

.github/workflows/pr-checks.yml

@@ -32,7 +32,7 @@ jobs:
         if: runner.os == 'Windows'
         run: git config --global core.autocrlf false
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Set up Node.js
         uses: actions/setup-node@v6
@@ -91,7 +91,7 @@ jobs:
       contents: read
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - id: head-version
         name: Verify all Actions use the same Node version
         run: |
@@ -106,7 +106,7 @@ jobs:
       - id: checkout-base
         name: 'Backport: Check out base ref'
         if: ${{ startsWith(github.head_ref, 'backport-') }}
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ env.BASE_REF }}