Bump actions/checkout from 2 to 4 (#319)

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/example-12.yml

@@ -27,7 +27,7 @@ jobs:
         solver: ["classic", "libmamba"]
         os: ["ubuntu-latest", "windows-latest"]
     steps:
-      - uses: actions/checkout@v2
+      - uses: actions/checkout@v4
       - uses: ./
         id: setup-miniconda
         continue-on-error: true