[web] make sure tests and benchmarks use correct backend - add autodetect false (#73047)

* add autodetect false

* fix typo
diff --git a/dev/bots/test.dart b/dev/bots/test.dart
index 78de4f2..211f522 100644
--- a/dev/bots/test.dart
+++ b/dev/bots/test.dart
@@ -997,6 +997,8 @@
         '--dart-define=FLUTTER_WEB_USE_SKIA=true',
       if (!canvasKit)
         '--dart-define=FLUTTER_WEB_USE_SKIA=false',
+      if (!canvasKit)
+        '--dart-define=FLUTTER_WEB_AUTO_DETECT=false',
       '--driver=test_driver/transitions_perf_e2e_test.dart',
       '--target=test_driver/transitions_perf_e2e.dart',
       '--browser-name=chrome',
@@ -1151,6 +1153,7 @@
       'chrome',
       '--web-run-headless',
       '--dart-define=FLUTTER_WEB_USE_SKIA=false',
+      '--dart-define=FLUTTER_WEB_AUTO_DETECT=false',
       ...additionalArguments,
       '-t',
       target,