[Test] Add a test case

Author: theblixguy

test/Concurrency/attr_discardableResult_async_await.swift

@@ -0,0 +1,11 @@
+// RUN: %target-typecheck-verify-swift  -disable-availability-checking
+// REQUIRES: concurrency
+
+// https://github.com/apple/swift/issues/60276
+
+@discardableResult @MainActor
+func mainActorAsyncDiscardable() async -> Int { 0 }
+
+func consumesMainActorAsyncDiscardable() async {
+  await mainActorAsyncDiscardable() // ok
+}