[Tests] Add REQUIRES: asserts to -swift-version 6 tests

Author: rintaro

test/Concurrency/actor_isolation_swift6.swift

@@ -1,5 +1,6 @@
 // RUN: %target-typecheck-verify-swift -disable-availability-checking -warn-concurrency -swift-version 6
 // REQUIRES: concurrency
+// REQUIRES: asserts
 
 final class ImmutablePoint: Sendable {
   let x : Int = 0

test/Concurrency/global_actor_inference_swift6.swift

@@ -2,6 +2,7 @@
 // RUN: %target-swift-frontend -swift-version 6 -emit-module -emit-module-path %t/other_global_actor_inference.swiftmodule -module-name other_global_actor_inference -warn-concurrency %S/Inputs/other_global_actor_inference.swift
 // RUN: %target-typecheck-verify-swift -swift-version 6 -I %t -disable-availability-checking
 // REQUIRES: concurrency
+// REQUIRES: asserts
 import other_global_actor_inference
 
 actor SomeActor { }