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/Clang.yml

@@ -22,7 +22,7 @@ jobs:
       image: ghcr.io/mattkretz/cplusplus-ci/base
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Run test suite
         env:

.github/workflows/GCC.yml

@@ -22,7 +22,7 @@ jobs:
       image: ghcr.io/mattkretz/cplusplus-ci/latest
 
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
 
       - name: Run test suite
         env:

.github/workflows/fair-software.yml

@@ -12,7 +12,7 @@ jobs:
     name: "fair-software"
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
         with:
           repository: mattkretz/howfairis
           path: howfairis

.github/workflows/reuse.yml

@@ -8,6 +8,6 @@ jobs:
   test:
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: REUSE Compliance Check
         uses: fsfe/reuse-action@v5