Bump dart-lang/setup-dart from 1.5.1 to 1.6.0

Bumps [dart-lang/setup-dart](https://github.com/dart-lang/setup-dart) from 1.5.1 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](dart-lang/setup-dart@8a4b97e...b64355a)

---
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>

.github/workflows/test-package.yml

@@ -23,7 +23,7 @@ jobs:
         sdk: [dev]
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
-      - uses: dart-lang/setup-dart@8a4b97ea2017cc079571daec46542f76189836b1
+      - uses: dart-lang/setup-dart@b64355ae6ca0b5d484f0106a033dd1388965d06d
         with:
           sdk: ${{ matrix.sdk }}
       - id: install
@@ -50,7 +50,7 @@ jobs:
         sdk: [2.19.0, dev]
     steps:
       - uses: actions/checkout@b4ffde65f46336ab88eb53be808477a3936bae11
-      - uses: dart-lang/setup-dart@8a4b97ea2017cc079571daec46542f76189836b1
+      - uses: dart-lang/setup-dart@b64355ae6ca0b5d484f0106a033dd1388965d06d
         with:
           sdk: ${{ matrix.sdk }}
       - id: install