Bump actions/checkout from 5 to 6

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]>

Author: dependabot[bot]

.github/workflows/dockertests.yml

@@ -11,7 +11,7 @@ jobs:
       matrix:
         docker-image: [debian, fedora, ubuntu, redhat]
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Setup docker container
       run: |
         docker build -t pyfakefs -f $GITHUB_WORKSPACE/.github/workflows/dockerfiles/Dockerfile_${{ matrix.docker-image }} . --build-arg github_repo=$GITHUB_REPOSITORY --build-arg github_branch=$GITHUB_REF_NAME

.github/workflows/release-deploy.yml

@@ -17,7 +17,7 @@ jobs:
         python-version: [ '3.10' ]
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
 
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v6

.github/workflows/testsuite.yml

@@ -12,7 +12,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Check out repository
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Set up Python
       uses: actions/setup-python@v6
       with:
@@ -38,7 +38,7 @@ jobs:
             os: ubuntu-latest
 
     steps:
-    - uses: actions/checkout@v5
+    - uses: actions/checkout@v6
     - name: Set up Python ${{ matrix.python-version }}
       uses: actions/setup-python@v6
       with:
@@ -116,7 +116,7 @@ jobs:
             pytest-version: 8.4.2
             os: windows-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with:
@@ -149,7 +149,7 @@ jobs:
         os: [ubuntu-latest, windows-latest]
         python-version:  ["3.13"]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Set up Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6
         with: