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](actions/checkout@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>

Author: dependabot[bot]

.github/workflows/check.yml

@@ -37,7 +37,7 @@ jobs:
         uses: actions/setup-python@v5
         with:
           python-version: "3.12"
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: Install tox
@@ -76,7 +76,7 @@ jobs:
           - { os: windows-latest, tox_env: pkg_meta } # would be the same
           - { os: ubuntu-latest, tox_env: docs } # runs on readthedocs.org already
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: Setup Python 3.12

.github/workflows/release.yml

@@ -18,7 +18,7 @@ jobs:
           python-version: "3.12"
       - name: Install build
         run: python -m pip install build
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0
       - name: Build package