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] <support@github.com>

Author: dependabot[bot]

.github/workflows/build-test-release.yml

@@ -31,7 +31,7 @@ jobs:
     name: Build sdist and set version
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: actions/setup-python@v6
         with:
@@ -77,7 +77,7 @@ jobs:
       HOMEBREW_FORCE_BREWED_CURL: 1
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Install packages
         run: |
           sudo apt-get update
@@ -108,7 +108,7 @@ jobs:
       PRESET: ${{ matrix.compiler }}-${{ matrix.build-option }}
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Activate conda
         uses: conda-incubator/setup-miniconda@v3  # install miniforge instead
@@ -161,7 +161,7 @@ jobs:
       PRESET: ci-clang-${{ matrix.build-option }}
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Set up XCode
         uses: maxim-lobanov/setup-xcode@v1
@@ -198,7 +198,7 @@ jobs:
     needs: [acquire-python-version-build-sdist]
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: actions/download-artifact@v6
         with:
@@ -247,7 +247,7 @@ jobs:
       run:
         shell: ${{ matrix.shell }}
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - uses: conda-incubator/setup-miniconda@v3
         with:
@@ -308,7 +308,7 @@ jobs:
           echo "Previous jobs have failures!"
           exit 1
 
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Setup python
         uses: actions/setup-python@v6

.github/workflows/check-code-quality.yml

@@ -25,7 +25,7 @@ jobs:
 
     steps:
       - name: Checkout
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Set up Python
         uses: actions/setup-python@v6

.github/workflows/citations.yml

@@ -30,7 +30,7 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
     - name: checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: Install R
       run: |
         sudo apt-get update && sudo apt-get install -y r-base

.github/workflows/clang-tidy.yml

@@ -48,7 +48,7 @@ jobs:
       HOMEBREW_FORCE_BREWED_CURL: 1
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Install packages
         run: |

.github/workflows/reuse-compliance.yml

@@ -19,6 +19,6 @@ jobs:
     runs-on: ubuntu-24.04
     steps:
     - name: checkout
-      uses: actions/checkout@v5
+      uses: actions/checkout@v6
     - name: REUSE Compliance Check
       uses: fsfe/reuse-action@v6

.github/workflows/sonar.yml

@@ -28,7 +28,7 @@ jobs:
       LLVM_COV: llvm-cov-18
       HOMEBREW_FORCE_BREWED_CURL: 1
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           fetch-depth: 0  # Shallow clones should be disabled for a better relevancy of analysis
       - name: Install packages