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/docs-build.yml

@@ -10,7 +10,7 @@ jobs:
     name: "Build"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python 3.12
         uses: actions/setup-python@v5

.github/workflows/python-publish.yml

@@ -15,7 +15,7 @@ jobs:
     permissions:
       id-token: write
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v5

.github/workflows/python-tests.yml

@@ -17,7 +17,7 @@ jobs:
         python-version: ['3.10', '3.11', '3.12', '3.13', '3.14']
       fail-fast: false
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v5
@@ -67,7 +67,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: "Checkout ${{ github.ref }} ( ${{ github.sha }} )"
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
 
       - name: "Setup Python"
         uses: actions/setup-python@v5