chore: bump actions/checkout from 5 to 6 in the actions group (#594)

Bumps the actions group with 1 update: [actions/checkout](https://github.com/actions/checkout).


Updates `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
  dependency-group: actions
...

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

Author: dependabot[bot]

.github/workflows/build-book.yml

@@ -15,7 +15,7 @@ jobs:
   build-test-book:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch_depth: 0
 

.github/workflows/crowdin_sync.yml

@@ -9,7 +9,7 @@ jobs:
 
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Sync with Crowdin
         uses: crowdin/github-action@v2