[Concurrency] Add a test case for passing a non-Sendable argument to a

nonisolated closure in an actor-isolated context.

(cherry picked from commit 9b16d47)

Author: hborla

test/Concurrency/sendable_checking.swift

@@ -249,7 +249,7 @@ func testConversionsAndSendable(a: MyActor, s: any Sendable, f: @Sendable () ->
 final class NonSendable {
   // expected-note @-1 3 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
   // SendNonSendable emits 3 fewer errors here.
-  // expected-targeted-and-complete-note @-3 3 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
+  // expected-targeted-and-complete-note @-3 4 {{class 'NonSendable' does not conform to the 'Sendable' protocol}}
   var value = ""
 
   @MainActor
@@ -284,3 +284,15 @@ func testNonSendableBaseArg() async {
   _ = await t.x
   // expected-warning @-1 {{non-sendable type 'NonSendable' passed in implicitly asynchronous call to main actor-isolated property 'x' cannot cross actor boundary}}
 }
+
+@available(SwiftStdlib 5.1, *)
+@MainActor
+func callNonisolatedAsyncClosure(
+  ns: NonSendable,
+  g: (NonSendable) async -> Void
+) async {
+  // FIXME: This should also produce a diagnostic with SendNonSendable, because
+  // the 'ns' parameter should be merged into the MainActor's region.
+  await g(ns)
+  // expected-targeted-and-complete-warning@-1 {{passing argument of non-sendable type 'NonSendable' outside of main actor-isolated context may introduce data races}}
+}