[web] add web-renderer option to flutter test. run web tests with this option (#73069)

* add web-renderer option to flutter test. run web tests with this option

* remove debug lines
diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 211f522..93ac203 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -1192,6 +1192,8 @@
         '--concurrency=1',  // do not parallelize on Cirrus, to reduce flakiness
       '-v',
       '--platform=chrome',
+      // TODO(ferhatb): Run web tests with both rendering backends.
+      '--web-renderer=html', // use html backend for web tests.
       '--sound-null-safety', // web tests do not autodetect yet.
       ...?flutterTestArgs,
       ...tests,