Bump actions/checkout from 3.5.2 to 3.6.0 (#301)

Bumps [actions/checkout](https://github.com/actions/checkout) from 3.5.2 to 3.6.0.
- [Release notes](https://github.com/actions/checkout/releases)
- [Changelog](https://github.com/actions/checkout/blob/main/CHANGELOG.md)
- [Commits](actions/checkout@8e5e7e5...f43a0e5)

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

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

.github/workflows/ci.yml

@@ -19,7 +19,7 @@ jobs:
     steps:
       # These are the latest versions of the github actions; dependabot will
       # send PRs to keep these up-to-date.
-      - uses: actions/checkout@8e5e7e5ab8b370d6c329ec480221332ada57f0ab
+      - uses: actions/checkout@f43a0e5ff2bd294095638e18286ca9a3d1956744
       - uses: dart-lang/setup-dart@d6a63dab3335f427404425de0fbfed4686d93c4f
         with:
           sdk: ${{ matrix.sdk }}