Fix test compatibility with Dart 3 (dart-lang/stream_transform#159)

Move opt out test to separate directory so they will not run by default.

Collapse the chrome and VM tests into a single workflow step.
Add a separate workflow step to run the chrome and VM opt out tests for
only the oldest supported SDK.

pkgs/stream_transform/.github/workflows/test-package.yml

diff --git a/pkgs/stream_transform/.github/workflows/test-package.yml b/pkgs/stream_transform/.github/workflows/test-package.yml
index 3aa30d4..ac6cb69 100644
--- a/pkgs/stream_transform/.github/workflows/test-package.yml
+++ b/pkgs/stream_transform/.github/workflows/test-package.yml
@@ -47,6 +47,7 @@
       matrix:
         # Add macos-latest and/or windows-latest if relevant for this package.
         os: [ubuntu-latest]
+        # Bump SDK for Legacy tets when changning min SDK.
         sdk: [2.14.0, dev]
     steps:
       - uses: actions/checkout@93ea575cb5d8a053eaa0ac8fa3b40d7e05a33cc8
@@ -56,9 +57,9 @@
       - id: install
         name: Install dependencies
         run: dart pub get
-      - name: Run VM tests
-        run: dart test --platform vm --test-randomize-ordering-seed=random
+      - name: Run tests
+        run: dart test -p chrome,vm --test-randomize-ordering-seed=random
         if: always() && steps.install.outcome == 'success'
-      - name: Run Chrome tests
-        run: dart test --platform chrome --test-randomize-ordering-seed=random
-        if: always() && steps.install.outcome == 'success'
+      - name: Run Legacy tests
+        run: dart test -p chrome,vm --test-randomize-ordering-seed=random legacy_test
+        if: always() && matrix.sdk == '2.14.0' && steps.install.outcome == 'success'

pkgs/stream_transform/legacy_test/opt_out_test.dart

diff --git a/pkgs/stream_transform/test/opt_out_test.dart b/pkgs/stream_transform/legacy_test/opt_out_test.dart
similarity index 100%
rename from pkgs/stream_transform/test/opt_out_test.dart
rename to pkgs/stream_transform/legacy_test/opt_out_test.dart