MAINTAINERS: add me as reviewer for sched_ext

Add me as a reviewer for sched_ext. I have been actively working on
the project and would like to help review patches and address related
kernel issues/features.

Signed-off-by: Changwoo Min <changwoo@igalia.com>
Signed-off-by: Tejun Heo <tj@kernel.org>

Author: multics69

MAINTAINERS

@@ -20903,6 +20903,7 @@ SCHEDULER - SCHED_EXT
 R:	Tejun Heo <tj@kernel.org>
 R:	David Vernet <void@manifault.com>
 R:	Andrea Righi <arighi@nvidia.com>
+R:	Changwoo Min <changwoo@igalia.com>
 L:	linux-kernel@vger.kernel.org
 S:	Maintained
 W:	https://github.com/sched-ext/scx