[Tests] NFC: Add a test-case for https://github.com/swiftlang/swift/issues/84509

Looks like the issue has been fixed already, so adding a
test-case to make sure that it doesn't regress in the future.

Resolves: https://github.com/swiftlang/swift/issues/84509
Resolves: rdar://161307898

test/Concurrency/attr_execution/issue-84509.swift

@@ -0,0 +1,30 @@
+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+// RUN: %target-swift-frontend(mock-sdk: %clang-importer-sdk) -emit-module %t/src/main.swift \
+// RUN:   -import-objc-header %t/src/Test.h \
+// RUN:   -swift-version 5 \
+// RUN:   -enable-upcoming-feature NonisolatedNonsendingByDefault \
+// RUN:   -module-name main -I %t -verify -verify-ignore-unrelated \
+// RUN:   -parse-as-library -o %t/main.o
+
+// REQUIRES: objc_interop
+// REQUIRES: swift_feature_NonisolatedNonsendingByDefault
+
+//--- Test.h
+@import Foundation;
+
+@protocol InterfaceT
+@end
+
+@interface Base : NSObject
+- (void)prepareWithP:(nullable id<InterfaceT>)p completionHandler:(void (^ _Nonnull)(NSError * _Nullable))completionHandler;
+@end
+
+//--- main.swift
+import Foundation
+
+class Derived : Base {
+  nonisolated(nonsending) override public func prepare(withP: (any InterfaceT)?) async throws {}
+}
+