Bump dart-lang/setup-dart from 1.6.2 to 1.6.4 (#322)

Bumps [dart-lang/setup-dart](https://github.com/dart-lang/setup-dart) from 1.6.2 to 1.6.4.
- [Release notes](https://github.com/dart-lang/setup-dart/releases)
- [Changelog](https://github.com/dart-lang/setup-dart/blob/main/CHANGELOG.md)
- [Commits](dart-lang/setup-dart@fedb126...f0ead98)

---
updated-dependencies:
- dependency-name: dart-lang/setup-dart
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

.github/workflows/ci.yml

@@ -20,7 +20,7 @@ jobs:
       # These are the latest versions of the github actions; dependabot will
       # send PRs to keep these up-to-date.
       - uses: actions/checkout@a5ac7e51b41094c92402da3b24376905380afc29
-      - uses: dart-lang/setup-dart@fedb1266e91cf51be2fdb382869461a434b920a3
+      - uses: dart-lang/setup-dart@f0ead981b4d9a35b37f30d36160575d60931ec30
         with:
           sdk: ${{ matrix.sdk }}
       - run: dart pub get