dashboard: update owners for host-linux-s390x
dashboard: update owners for host-linux-s390x

Update the owners for host-linux-s390x as
Peter (ruixin-bao) will be leaving IBM.

Change-Id: I549b14872f5cb6ecb1ef27e90b3e5f02d4854726
Reviewed-on: https://go-review.googlesource.com/c/build/+/370879
Auto-Submit: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Run-TryBot: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Run-TryBot: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@google.com>
Reviewed-by: Dmitri Shuralyov <d181b7fea0ec87c86ba5a890ab716db52498e3ba@golang.org>
Reviewed-by: Ruixin Bao <bce0ef09ffdb0b0b071ab8c3e5befbf94c7e2380@gmail.com>
TryBot-Result: Gopher Robot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Bryan Mills <1c8aad60184261ccede67f5c63a0d2a3bf3c9ff4@google.com>

golang/build,golang/build,golang/build,golang/build