build(deps): 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](https://github.com/actions/checkout/compare/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>

.github/workflows/unit-tests.yml

@@ -70,7 +70,7 @@ jobs:
 
     steps:
       - name: checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: install system requirements
         run: |
@@ -151,7 +151,7 @@ jobs:
   collect-and-verify:
     runs-on: ubuntu-24.04
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: Setup Python
         uses: actions/setup-python@v6
         with:
@@ -227,7 +227,7 @@ jobs:
     runs-on: ubuntu-24.04
     needs: [run-tests]
     steps:
-      - uses: actions/checkout@v5
+      - uses: actions/checkout@v6
       - name: collect pytest warnings files
         uses: actions/download-artifact@v5
         with:
@@ -280,7 +280,7 @@ jobs:
           - 3.11
     steps:
       - name: Checkout repo
-        uses: actions/checkout@v5
+        uses: actions/checkout@v6
 
       - name: Setup Python ${{ matrix.python-version }}
         uses: actions/setup-python@v6