Adjust test configs

- Disable web plugin implementation package Dart tests on Windows hosts;
  that config has never been supported.
- Split Linux Dart unit tests into two shards, since tehy are now quite
  long.
- Disable `flutter_migrate` Dart tests on the Windows host, for time.
- Temporarily disable a failing test on `stable`, with a TODO+issue.

Author: stuartmorgan-g

.cirrus.yml

@@ -235,6 +235,9 @@ task:
     ### Platform-agnostic tasks ###
     - name: dart_unit_tests
       env:
+        matrix:
+          PACKAGE_SHARDING: "--shardIndex 0 --shardCount 2"
+          PACKAGE_SHARDING: "--shardIndex 1 --shardCount 2"
         matrix:
           CHANNEL: "master"
           CHANNEL: "stable"
@@ -315,7 +318,13 @@ task:
       build_script:
         - ./script/tool_runner.sh build-examples --web
       drive_script:
-        - ./script/tool_runner.sh drive-examples --web --exclude=script/configs/exclude_integration_web.yaml
+        # TODO(stuartmorgan): Figure out why url_launcher_web is failing on stable and re-enable it:
+        # https://github.com/flutter/flutter/issues/121161
+        - if [[ "$CHANNEL" == "master" ]]; then
+        -   ./script/tool_runner.sh drive-examples --web --exclude=script/configs/exclude_integration_web.yaml
+        - else
+        -   ./script/tool_runner.sh drive-examples --web --exclude=script/configs/exclude_integration_web.yaml,url_launcher_web
+        - fi
     - name: web_benchmarks_test
       env:
         matrix:

script/configs/windows_unit_tests_exceptions.yaml

@@ -1,4 +1,16 @@
 # Packages that are excluded from dart unit test on Windows.
-
 # Exclude flutter_image because its tests need a test server, so are run via custom_package_tests.
 - flutter_image
+# This test is very slow, so isn't worth running a second time
+# on Windows; the Linux run is enough coverage.
+- flutter_migrate
+# Windows infra currently isn't set up to run web package unit tests.
+- camera_web
+- file_selector_web
+- google_maps_flutter_web
+- google_sign_in_web
+- image_picker_for_web
+- shared_preferences_web
+- url_launcher_web
+- video_player_web
+- webview_flutter_web