Fix pub tests.

sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart

Index: sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart
diff --git a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart
index 0a61e5945598c661b30fad3e551dc76b5030e6d4..ae98d6685ecb33df2a2c9c4988d5ac770c29c02a 100644
--- a/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart
+++ b/sdk/lib/_internal/pub/test/transformer/fails_to_load_a_transform_with_a_syntax_error_test.dart
@@ -31,8 +31,7 @@ main() {
       createLockFile('myapp', pkg: ['barback']);
 
       var pub = startPubServe();
-      pub.stderr.expect('[RewriteImport]:');
-      pub.stderr.expect(startsWith('Error in'));
+      pub.stderr.expect(contains("unexpected token 'syntax'"));
       pub.shouldExit(1);
       pub.stderr.expect(never(contains('This is an unexpected error')));
     });