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](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/build.yml

@@ -49,7 +49,7 @@ jobs:
       - uses: hmarr/debug-action@v3
       - name: Cancel Workflow Action
         uses: styfle/cancel-workflow-action@0.12.1
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: ccache
         if: matrix.os != 'ubuntu-24.04-arm'
         uses: hendrikmuhs/ccache-action@v1.2
@@ -108,7 +108,7 @@ jobs:
     name: Make SDist
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Build SDist
       run: pipx run build --sdist

.github/workflows/cache-maintenance.yml

@@ -11,7 +11,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Check out code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Cleanup
         run: |