[Tests] Temporarily disable flakey async taskgroup test

Test was previously disabled for ASAN, but it is also failing on regular
builds. Disable until it can be looked into.

Author: bnbarham

test/Concurrency/Runtime/async_taskgroup_throw_rethrow.swift

@@ -4,8 +4,7 @@
 // REQUIRES: OS=macosx
 // REQUIRES: CPU=x86_64
 
-// Remove with rdar://problem/73154198
-// UNSUPPORTED: asan
+// REQUIRES: rdar73154198
 
 import Dispatch