Bump actions/checkout from 5 to 6 (#482)

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

@@ -20,7 +20,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout Code
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Run markdownlint-cli
         uses: nosborn/[email protected]
         with:
@@ -38,7 +38,7 @@ jobs:
           - '3.12'
           - '3.13'
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python
         uses: actions/setup-python@v6
         with:

.github/workflows/release.yml

@@ -17,7 +17,7 @@ jobs:
     if: ${{ github.event.workflow_run.conclusion == 'success' && github.event.workflow_run.event == 'push' && startsWith(github.event.workflow_run.head_branch, 'v') }}
     steps:
       - name: Check out the repository including tags
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
         with:
           ref: ${{ github.event.workflow_run.head_sha }}
           fetch-depth: 0
@@ -51,7 +51,7 @@ jobs:
     runs-on: ubuntu-latest
     if: ${{ needs.validate-tag.outputs.valid_tag == 'true' && github.event.workflow_run.conclusion == 'success' }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v6

.github/workflows/sync-test-fixtures.yml

@@ -10,7 +10,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout repository
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
       - name: Sync fixtures
         run: |
           TMP_DIR=$(mktemp -d)