make sure tests and becnhmarks use correct backend (#72628)

dev/bots/test.dart

diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 2a9d49f..f302ee2 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -995,6 +995,8 @@
       'drive',
       if (canvasKit)
         '--dart-define=FLUTTER_WEB_USE_SKIA=true',
+      if (!canvasKit)
+        '--dart-define=FLUTTER_WEB_USE_SKIA=false',
       '--driver=test_driver/transitions_perf_e2e_test.dart',
       '--target=test_driver/transitions_perf_e2e.dart',
       '--browser-name=chrome',