Fix missing curly brace in TaskLocal documentation

Author: Kyle-Ye

stdlib/public/Concurrency/TaskLocal.swift

@@ -100,6 +100,7 @@ public macro TaskLocal() =
 ///     func enter() {
 ///         Example.$traceID.withValue("1234") {
 ///             read() // always "1234", regardless if enter() was called from inside a task or not:
+///         }    
 ///     }
 ///    
 ///     func read() -> String {