Bump actions/checkout from 5.0.1 to 6.0.0 (#1461)

Bumps [actions/checkout](https://github.com/actions/checkout) from 5.0.1 to 6.0.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Commits](actions/checkout@v5.0.1...v6)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-version: 6.0.0
  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

@@ -50,7 +50,7 @@ jobs:
           - {VERSION: "3.13", NOXSESSION: "mypy"}
           - {VERSION: "3.9", NOXSESSION: "docs"}
     steps:
-      - uses: actions/checkout@v5.0.1
+      - uses: actions/checkout@v6.0.0
       - name: Setup python
         uses: actions/setup-python@v6
         with:
@@ -72,7 +72,7 @@ jobs:
           - {CONTAINER: "ubuntu-rolling", NOXSESSION: "tests-cryptography-main"}
     name: "${{ matrix.TEST.NOXSESSION }} on ${{ matrix.TEST.CONTAINER }}"
     steps:
-      - uses: actions/checkout@v5.0.1
+      - uses: actions/checkout@v6.0.0
       - run: /venv/bin/pip install nox
       - run: /venv/bin/nox
         env:
@@ -93,7 +93,7 @@ jobs:
           - 3.12
     name: "Downstream tests for ${{ matrix.DOWNSTREAM }}"
     steps:
-      - uses: actions/checkout@v5.0.1
+      - uses: actions/checkout@v6.0.0
       - name: Setup python
         uses: actions/setup-python@v6
         with: