Mark a test as skipped.

The test is broken by dart-lang/sdkdart-lang/glob#28015.

pkgs/glob/test/list_test.dart

diff --git a/pkgs/glob/test/list_test.dart b/pkgs/glob/test/list_test.dart
index 869b49d..9a389e8 100644
--- a/pkgs/glob/test/list_test.dart
+++ b/pkgs/glob/test/list_test.dart
@@ -302,7 +302,7 @@
         p.join("foo", "baz", "bang"),
         p.join("foo", "baz", "qux")
       ])));
-    });
+    }, skip: "Broken by sdk#28015.");
 
     test("lists a subdirectory that sometimes exists", () {
       d.dir("top", [