chore(deps): 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/ci.yaml

@@ -19,7 +19,7 @@ jobs:
     runs-on: ubuntu-22.04
     steps:
       - name: Checkout main
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: Setup Python
         uses: actions/setup-python@v5

.github/workflows/link-check.yaml

@@ -31,7 +31,7 @@ jobs:
             echo "MOD_ONLY=yes" >> "$GITHUB_OUTPUT"
           fi
       - name: Checkout repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Check markdown links
         uses: gaurav-nelson/github-action-markdown-link-check@v1
         with:

.github/workflows/spellcheck.yaml

@@ -20,7 +20,7 @@ jobs:
     name: Spellcheck
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
       - name: Run spellcheck
         uses: tbroadley/spellchecker-cli-action@v1
         with: