Fix an iterable_contains_unrelated_type warning.

Change-Id: Ie9b5ff4298b1213ccec8764728a9a40475e56603
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/193340
Commit-Queue: Devon Carew <devoncarew@google.com>
Reviewed-by: Bob Nystrom <rnystrom@google.com>

pkg/test_runner/lib/src/testing_servers.dart

@@ -7,7 +7,6 @@ import 'dart:convert' show HtmlEscape;
 import 'dart:io';
 
 import 'package:package_config/package_config.dart';
-
 import 'package:test_runner/src/configuration.dart';
 import 'package:test_runner/src/repository.dart';
 import 'package:test_runner/src/utils.dart';

tools/bots/test_matrix.json

@@ -3303,6 +3303,7 @@
           "script": "out/ReleaseX64/dart-sdk/bin/dart",
           "arguments": [
             "analyze",
+            "--fatal-infos",
             "pkg/test_runner"
           ]
         },