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/ci.yml

@@ -17,7 +17,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Lint with Ruff
       uses: astral-sh/ruff-action@v3
     - name: Format with Ruff
@@ -29,7 +29,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install uv
       uses: astral-sh/setup-uv@v7
     - name: Set up Python
@@ -71,7 +71,7 @@ jobs:
       fail-fast: false
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Set up OpenFOAM
       uses: gerlero/setup-openfoam@v1
       with:
@@ -104,7 +104,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install uv
       uses: astral-sh/setup-uv@v7
     - name: Check package build

.github/workflows/dockerhub-description.yml

@@ -16,7 +16,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Modify README.md for Docker Hub
       run: |
         sed -i "s|^\s*#\s\+\(.\+\)|# [\1]($GITHUB_SERVER_URL/$GITHUB_REPOSITORY)|" README.md

.github/workflows/pypi-publish.yml

@@ -15,7 +15,7 @@ jobs:
 
     steps:
     - name: Checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install uv
       uses: astral-sh/setup-uv@v7
     - name: Build