Update xml/issue4445.xml

Author: Dani-Hub

xml/issue4445.xml

@@ -42,7 +42,7 @@ namespace std::execution {
     explicit task_scheduler(Sch&& sch, Allocator alloc = {});
 
     <ins>task_scheduler(const task_scheduler&amp;) = default;</ins>
-    <ins>task_scheduler& operator=(const task_scheduler&amp;) = default;</ins>
+    <ins>task_scheduler&amp; operator=(const task_scheduler&amp;) = default;</ins>
 
     <i>ts-sender</i> schedule();