Rollup merge of rust-lang#142744 - tgross35:y21-mailmap, r=y21

Add a mailmap entry for y21

Author: Kobzol

.mailmap

@@ -698,3 +698,4 @@ Zach Pomerantz <zmp@umich.edu>
 Zack Corr <zack@z0w0.me> <zackcorr95@gmail.com>
 Zack Slayton <zack.slayton@gmail.com>
 Zbigniew Siciarz <zbigniew@siciarz.net> Zbigniew Siciarz <antyqjon@gmail.com>
+y21 <30553356+y21@users.noreply.github.com>