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

* add autodetect false

* fix typo

Author: nturgut

dev/bots/test.dart

@@ -997,6 +997,8 @@ Future<void> _runGalleryE2eWebTest(String buildMode, { bool canvasKit = false })
         '--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 @@ Future<void> _runWebDebugTest(String target, {
       'chrome',
       '--web-run-headless',
       '--dart-define=FLUTTER_WEB_USE_SKIA=false',
+      '--dart-define=FLUTTER_WEB_AUTO_DETECT=false',
       ...additionalArguments,
       '-t',
       target,

dev/devicelab/lib/tasks/web_benchmarks.dart

@@ -31,6 +31,8 @@ Future<TaskResult> runWebBenchmark({ @required bool useCanvasKit }) async {
       '--dart-define=FLUTTER_WEB_ENABLE_PROFILING=true',
       if (!useCanvasKit)
         '--dart-define=FLUTTER_WEB_USE_SKIA=false',
+      if (!useCanvasKit)
+        '--dart-define=FLUTTER_WEB_AUTO_DETECT=false',
       if (useCanvasKit)
         '--dart-define=FLUTTER_WEB_USE_SKIA=true',
       '--profile',