[DOC] Move Therad#join under Thread in NEWS-3.0.0.md

Author: znz

doc/NEWS/NEWS-3.0.0.md

@@ -367,11 +367,11 @@ Outstanding ones only.
     * Fiber.blocking? tells whether the current execution context is
       blocking. [[Feature #16786]]
 
+* Thread
+
     * Thread#join invokes the scheduler hooks `block`/`unblock` in a
       non-blocking execution context. [[Feature #16786]]
 
-* Thread
-
     * Thread.ignore_deadlock accessor has been added for disabling the
       default deadlock detection, allowing the use of signal handlers to
       break deadlock. [[Bug #13768]]