Bump actions/checkout from 4 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 4 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v4...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/check-links.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       # Checks out a copy of your repository on the ubuntu-latest machine
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           # Make sure the actual branch is checked out when running on PR
           # ref: ${{ github.event.pull_request.head.sha }}

.github/workflows/lint.yml

@@ -13,7 +13,7 @@ jobs:
     steps:
       # Checks out a copy of your repository on the ubuntu-latest machine
       - name: Checkout code
-        uses: actions/checkout@v4
+        uses: actions/checkout@v6
         with:
           # Make sure the actual branch is checked out when running on PR
           # ref: ${{ github.event.pull_request.head.sha }}

.github/workflows/pytest.yaml

@@ -12,7 +12,7 @@ jobs:
     name: Test itwinai with pytest
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v4
+      - uses: actions/checkout@v6
 
       - name: Install plugin dependencies
         shell: bash -l {0}