[testing] Add missing REQUIRES: concurrency

Author: davezarzycki

test/Serialization/actor-attr-query-cycle.swift

@@ -4,6 +4,8 @@
 // RUN: %target-swift-frontend -emit-module -o %t/b.swiftmodule -emit-module-source-info-path %t/b.swiftsourceinfo -primary-file %S/Inputs/actor_bar.swift %s -module-name Foo
 // RUN: %target-swift-frontend -merge-modules -emit-module -o %t/Foo.swiftmodule  -emit-module-source-info-path %t/Foo.swiftsourceinfo %t/a.swiftmodule %t/b.swiftmodule -module-name Foo
 
+// REQUIRES: concurrency
+
 extension Bar {
   @MainActor
   func bar() async throws -> Int {