Bump actions/checkout from 2 to 4 (#356)

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>

Author: dependabot[bot]

.github/workflows/main.yml

@@ -21,7 +21,7 @@ jobs:
         include:
           - cache-key: 'stable'
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - name: Checkout submodules
         run: git submodule update --init --recursive