⬆️ Bump actions/checkout from 5 to 6 (#160)

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -12,7 +12,7 @@ jobs:
   pre-commit:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up Python 3.11
       uses: actions/setup-python@v6
       with:
@@ -27,7 +27,7 @@ jobs:
         sphinx: [">=5,<6"]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with:
@@ -54,7 +54,7 @@ jobs:
     name: Documentation build
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python 3.11
         uses: actions/setup-python@v6
         with:
@@ -76,7 +76,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout source
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Set up Python 3.11
         uses: actions/setup-python@v6
         with: