Bump dart-lang/setup-dart from 1.5.0 to 1.6.0 (#305)

Bumps [dart-lang/setup-dart](https://github.com/dart-lang/setup-dart) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/dart-lang/setup-dart/releases)
- [Changelog](https://github.com/dart-lang/setup-dart/blob/main/CHANGELOG.md)
- [Commits](https://github.com/dart-lang/setup-dart/compare/d6a63dab3335f427404425de0fbfed4686d93c4f...b64355ae6ca0b5d484f0106a033dd1388965d06d)

---
updated-dependencies:
- dependency-name: dart-lang/setup-dart
  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>
diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index d4470df..a867cb0 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -20,7 +20,7 @@
       # These are the latest versions of the github actions; dependabot will
       # send PRs to keep these up-to-date.
       - uses: actions/checkout@8ade135a41bc03ea155e62e844d188df1ea18608
-      - uses: dart-lang/setup-dart@d6a63dab3335f427404425de0fbfed4686d93c4f
+      - uses: dart-lang/setup-dart@b64355ae6ca0b5d484f0106a033dd1388965d06d
         with:
           sdk: ${{ matrix.sdk }}
       - run: dart pub get