Use typed throws in withSerialExecutor

Author: ktoso

proposals/0471-SerialExecutor-isIsolated.md

@@ -150,7 +150,7 @@ extension Actor {
   /// of the executor while performing the operation.
   @_alwaysEmitIntoClient
   @available(SwiftStdlib 5.1, *)
-  public nonisolated func withSerialExecutor<T>(_ operation: (any SerialExecutor) throws -> T) rethrows -> T
+  public nonisolated func withSerialExecutor<T, E: Error>(_ operation: (any SerialExecutor) throws(E) -> T) throws(E) -> T
 
   /// Perform an operation with the actor's ``SerialExecutor``.
   ///
@@ -159,7 +159,7 @@ extension Actor {
   /// of the executor while performing the operation.
   @_alwaysEmitIntoClient
   @available(SwiftStdlib 5.1, *)
-  public nonisolated func withSerialExecutor<T>(_ operation: (any SerialExecutor) async throws -> T) async rethrows -> T
+  public nonisolated func withSerialExecutor<T, E: Error>(_ operation: (any SerialExecutor) async throws(E) -> T) async throws(E) -> T
 
 }
 ```