[Concurrency] %import dispatch for Linux startSynchronously test

Author: ktoso

stdlib/public/Concurrency/Actor.cpp

@@ -2311,7 +2311,7 @@ static void swift_task_switchImpl(SWIFT_ASYNC_CONTEXT AsyncContext *resumeContex
                        currentTaskExecutor.isDefined() ? "" : " (undefined)",
                        newTaskExecutor.getIdentity(),
                        newTaskExecutor.isDefined() ? "" : " (undefined)",
-                       trackingInfo->isSynchronousStart() ? "[synchronous start]" : "[NOT SYNC START]");
+                       trackingInfo->isSynchronousStart() ? "[synchronous start]" : "");
 
   // If the current executor is compatible with running the new executor,
   // we can just immediately continue running with the resume function

stdlib/public/Concurrency/Task+startSynchronously.swift.gyb

@@ -52,7 +52,7 @@ extension Task where Failure == ${FAILURE_TYPE} {
   ///   - priority: The priority of the task.
   ///     Pass `nil` to use the ``Task/basePriority`` of the current task (if there is one).
   ///   - operation: the operation to be run immediately upon entering the task.
-  /// - Returns:
+  /// - Returns: A reference to the unstructured task which may be awaited on.
   @available(SwiftStdlib 6.2, *)
   @discardableResult
   public static func _startSynchronously(

test/Concurrency/Runtime/startSynchronously.swift

@@ -1,5 +1,5 @@
 // RUN: %empty-directory(%t)
-// RUN: %target-build-swift -Xfrontend -disable-availability-checking %s -swift-version 6 -o %t/a.out
+// RUN: %target-build-swift -Xfrontend -disable-availability-checking %s %import-libdispatch -swift-version 6 -o %t/a.out
 // RUN: %target-codesign %t/a.out
 // RUN: %target-run %t/a.out | %FileCheck %s --dump-input=always