Install a Flutter SDK in the publish workflow (#141)

Author: sigurdm

.github/workflows/publish.yml

@@ -29,8 +29,16 @@ jobs:
     steps:
       # Checkout repository
       - uses: actions/checkout@v4
-      # Setup Dart SDK with JWT token
+      # Set up the Dart SDK and provision the OIDC token used for publishing.
+      # The `dart` command from this step will be shadowed by the one from the
+      # Flutter SDK below. 
       - uses: dart-lang/setup-dart@0a8a0fc875eb934c15d08629302413c671d3f672
+      # Download flutter SDK - needed for publishing Flutter packages. Can also
+      # publish pure Dart packages.
+      #
+      # The dart binary from a Flutter SDK facilitates publishing both Flutter
+      # and pure-dart packages.
+      - uses: flutter-actions/setup-flutter@d030cb603380106494f72d65a7e52462f380781f
       # Minimal package setup and dry run checks.
       - name: Install dependencies
         run: dart pub get