dashboard: change owner for host-linux-s390x

This CL changes the owner for host-linux-s390x as
Michael will be leaving IBM at the end of this week.

See https://groups.google.com/g/golang-dev/c/obUDaYbaxXw.

Change-Id: Ic140743387cff02be7c0471f803c5a30d812d0c3
Reviewed-on: https://go-review.googlesource.com/c/build/+/274512
Reviewed-by: Michael Munday <michael.munday@live.co.uk>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
Trust: Michael Munday <michael.munday@live.co.uk>
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
TryBot-Result: Go Bot <gobot@golang.org>
diff --git a/dashboard/builders.go b/dashboard/builders.go
index 332dd48..c31978e 100644
--- a/dashboard/builders.go
+++ b/dashboard/builders.go
@@ -513,7 +513,7 @@
 	},
 	"host-linux-s390x": &HostConfig{
 		Notes:       "run by IBM",
-		OwnerGithub: "mundaym",
+		OwnerGithub: "ruixin-bao",
 		IsReverse:   true,
 		env:         []string{"GOROOT_BOOTSTRAP=/var/buildlet/go-linux-s390x-bootstrap"},
 	},