[flutter_tools] remove await runZonedGuarded() in tests (#142336)

For context https://github.com/flutter/flutter/issues/142338

packages/flutter_tools/test/general.shard/resident_runner_test.dart

@@ -2130,10 +2130,10 @@ flutter:
       vmServiceUris: Stream<Uri>.value(testUri),
     );
     final Completer<void> done = Completer<void>();
-    await runZonedGuarded(
+    unawaited(runZonedGuarded(
       () => flutterDevice.connect(allowExistingDdsInstance: true).then((_) => done.complete()),
       (_, __) => done.complete(),
-    );
+    ));
     await done.future;
     expect(device.dds.uri, Uri.parse('http://localhost/existingDdsInField'));
   }, overrides: <Type, Generator>{
@@ -2164,10 +2164,10 @@ flutter:
       vmServiceUris: Stream<Uri>.value(testUri),
     );
     final Completer<void>done = Completer<void>();
-    await runZonedGuarded(
+    unawaited(runZonedGuarded(
       () => flutterDevice.connect(allowExistingDdsInstance: true).then((_) => done.complete()),
       (_, __) => done.complete(),
-    );
+    ));
     await done.future;
     expect(device.dds.uri, Uri.parse('http://localhost/existingDdsInMessage'));
   }, overrides: <Type, Generator>{