Bump actions/checkout from 5 to 6 (#97)

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

Author: dependabot[bot]

.github/workflows/ci.yml

@@ -9,7 +9,7 @@ jobs:
   build:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depth: 0
     - uses: actions/setup-dotnet@v5
@@ -26,7 +26,7 @@ jobs:
   lint:
     runs-on: ubuntu-latest
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
       with:
         fetch-depths: 0
     - uses: astral-sh/setup-uv@v7
@@ -80,7 +80,7 @@ jobs:
       run: |
         choco install -y mono ${{ matrix.python == 'pypy3' && '--x86' || '' }}
 
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Install dependencies
       run: |

.github/workflows/docs.yml

@@ -7,7 +7,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - uses: astral-sh/setup-uv@v7
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Build Sphinx documentation
       run: |