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](actions/checkout@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] <[email protected]>

Author: dependabot[bot]

.github/workflows/CI.yml

@@ -15,7 +15,7 @@ jobs:
     runs-on: ubuntu-latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - uses: iterate-ch/[email protected]
         with:
           docs-folder: "."
@@ -32,7 +32,7 @@ jobs:
     needs: build
     if: github.ref == 'refs/heads/main'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Cache artifacts
         uses: actions/cache@v4
         with:

.github/workflows/codespell.yml

@@ -17,6 +17,6 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Codespell
         uses: codespell-project/actions-codespell@v2