[dashboard] Update tree favicons (#1885)

diff --git a/auto_submit/test/requests/check_pull_request_test.dart b/auto_submit/test/requests/check_pull_request_test.dart
index db0d2b0..305222e 100644
--- a/auto_submit/test/requests/check_pull_request_test.dart
+++ b/auto_submit/test/requests/check_pull_request_test.dart
@@ -18,7 +18,6 @@
 
 import '../utilities/mocks.dart';
 import './github_webhook_test_data.dart';
-import '../requests/github_webhook_test_data.dart';
 import '../src/request_handling/fake_pubsub.dart';
 import '../src/request_handling/fake_authentication.dart';
 import '../src/service/fake_config.dart';
diff --git a/dashboard/web/favicon-failure.png b/dashboard/web/favicon-failure.png
index 7443f05..7324909 100644
--- a/dashboard/web/favicon-failure.png
+++ b/dashboard/web/favicon-failure.png
Binary files differ
diff --git a/dashboard/web/favicon.png b/dashboard/web/favicon.png
index 8aaa46a..f75e7a2 100644
--- a/dashboard/web/favicon.png
+++ b/dashboard/web/favicon.png
Binary files differ