MAINTAINERS: add regressions mailing list

Add the newly created regression mailing list finally created after it
already had been agreed on during the maintainers summit 2017 (see
https://lwn.net/Articles/738216/ ). The topic was recently discussed
again, where an idea to create a broader list for all issues was
discussed, but Linus preferred a more targeted list:
https://lkml.kernel.org/r/CAHk-=wgiYqqLzsb9-UpfH+=ktk7ra-2fOsdc_ZJ7WF47wS73CA@mail.gmail.com/

Hence, the creation for that list was asked for and granted:
https://bugzilla.kernel.org/show_bug.cgi?id=212557

In the end it became regressions@lists.linux.dev instead of
linux-regressions@lists.linux.dev as 'Linux' would have been redundant
in the latter case.
Signed-off-by: Thorsten Leemhuis <linux@leemhuis.info>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Link: https://lore.kernel.org/r/ecf1f0125399c5242ff213b827eacc6f93af3172.1617967127.git.linux@leemhuis.infoSigned-off-by: Jonathan Corbet <corbet@lwn.net>

MAINTAINERS

@@ -9730,6 +9730,11 @@ F:	include/uapi/linux/sunrpc/
 F:	net/sunrpc/
 F:	Documentation/filesystems/nfs/
 
+KERNEL REGRESSIONS
+M:	Thorsten Leemhuis <linux@leemhuis.info>
+L:	regressions@lists.linux.dev
+S:	Supported
+
 KERNEL SELFTEST FRAMEWORK
 M:	Shuah Khan <shuah@kernel.org>
 M:	Shuah Khan <skhan@linuxfoundation.org>