MAINTAINERS: Assign hsr selftests to HSR

Despite the HSR subsystem being orphaned at the moment due to the original
maintainer being unreachable for a while, assign the selftests to the
subsystem for the future.

Signed-off-by: Felix Maurer <fmaurer@redhat.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Link: https://patch.msgid.link/f4a356b96f5e0c99d9db3984ea62596c99a97469.1770299429.git.fmaurer@redhat.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>

Author: fmaurer-rh

MAINTAINERS

@@ -11592,6 +11592,7 @@ HSR NETWORK PROTOCOL
 L:	netdev@vger.kernel.org
 S:	Orphan
 F:	net/hsr/
+F:	tools/testing/selftests/net/hsr/
 
 HT16K33 LED CONTROLLER DRIVER
 M:	Robin van der Gracht <robin@protonic.nl>