Merge pull request #83330 from al45tair/eng/PR-156710569

[Concurrency] Update availability of UnimplementedExecutor.

Author: al45tair

stdlib/public/Concurrency/UnimplementedExecutor.swift

@@ -14,7 +14,7 @@ import Swift
 
 // .. Main Executor ............................................................
 
-@available(SwiftStdlib 6.2, *)
+@available(StdlibDeploymentTarget 6.2, *)
 public final class UnimplementedMainExecutor: MainExecutor, @unchecked Sendable {
   public init() {}
 
@@ -45,7 +45,7 @@ public final class UnimplementedMainExecutor: MainExecutor, @unchecked Sendable
 
 // .. Task Executor ............................................................
 
-@available(SwiftStdlib 6.2, *)
+@available(StdlibDeploymentTarget 6.2, *)
 public final class UnimplementedTaskExecutor: TaskExecutor, @unchecked Sendable {
   public init() {}