Bump actions/checkout from 2 to 4 (#20)

Bumps [actions/checkout](https://github.com/actions/checkout) from 2 to 4.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@v2...v4)

---
updated-dependencies:
- dependency-name: actions/checkout
  dependency-type: direct:production
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

.github/workflows/CI.yml

@@ -29,7 +29,7 @@ jobs:
           - x86
           - x64
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: julia-actions/setup-julia@v1
         with:
           version: ${{ matrix.version }}
@@ -50,7 +50,7 @@ jobs:
 #      contents: write
 #      statuses: write
 #    steps:
-#      - uses: actions/checkout@v2
+#      - uses: actions/checkout@v4
 #      - uses: julia-actions/setup-julia@v1
 #        with:
 #          version: '1'