Bump actions/checkout from 2 to 6

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 6.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...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/CI.yml

@@ -28,7 +28,7 @@ jobs:
           - x64
     steps:
       - name: Checkout repository for access
-        uses: actions/checkout@v2
+        uses: actions/checkout@v6
 
       - name: Setup Julia
         uses: julia-actions/setup-julia@v1
@@ -61,7 +61,7 @@ jobs:
       contents: write
       statuses: write
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v6
       - uses: julia-actions/setup-julia@v1
         with:
           version: '1'