Try updating setup-dart (#2807)

Author: jcollins-g

.github/workflows/test.yaml

@@ -64,7 +64,7 @@ jobs:
         if: runner.os == 'Windows'
         run: git config --global core.autocrlf input
       - uses: actions/checkout@v2
-      - uses: dart-lang/setup-dart@v1.0
+      - uses: dart-lang/setup-dart@v1.2
         with:
           sdk: ${{ matrix.sdk }}
       - name: Install dependencies