build(deps): bump dart-lang/setup-dart from 1.7.2 to 1.8.1 (#471)

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

Author: dependabot[bot]

.github/workflows/tests.yml

@@ -20,7 +20,7 @@ jobs:
           - stable
     steps:
       - uses: actions/checkout@v7.0.1
-      - uses: dart-lang/setup-dart@v1.7.2
+      - uses: dart-lang/setup-dart@v1.8.1
         with:
           sdk: "${{ matrix.sdk }}"
       - name: Install dependencies