dartdev: skip 'pub outdated' check in tests

Fixes https://github.com/dart-lang/sdk/issues/42049

We should enable, and test this feature in these tests, I think.
But for now I just need the tests to start passing. I haven't wrapped
my head around how mock-y / end-to-end-y migrate_test is.

Change-Id: I7a2e2034b2a1f42b71d78f4776ee8711071f01f7
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/149200
Commit-Queue: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Mike Fairhurst <mfairhurst@google.com>

pkg/dartdev/test/utils.dart

@@ -58,12 +58,12 @@ class TestProject {
     var arguments = [
       absolutePathToDartdevFile,
       command,
+      if (command == 'migrate')
+        // TODO(srawlins): Enable `pub outdated` in tests.
+        '--skip-pub-outdated',
+      ...?args,
     ];
 
-    if (args != null && args.isNotEmpty) {
-      arguments.addAll(args);
-    }
-
     return Process.runSync(
       Platform.resolvedExecutable,
       arguments,