Add Lu Yahan to RISC-V owners list

Lu Yahan is a key contributor to the RISC-V target and I would like to
add him to the owners list so that he can approve changes in Gerrit.

Change-Id: I017fb2ef20320887959e9830fb63e05df121c7b9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3145370Reviewed-by: Ji Qiu <qiuji@iscas.ac.cn>
Reviewed-by: Hannes Payer <hpayer@chromium.org>
Commit-Queue: Brice Dobry <brice.dobry@futurewei.com>
Cr-Commit-Position: refs/heads/main@{#76800}

RISCV_OWNERS

 brice.dobry@futurewei.com
 peng.w@rioslab.org
 qiuji@iscas.ac.cn
+yahan@iscas.ac.cn