.mailmap: add an alias for Sergii Romantsov

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index f2a0fdc..a71ad44 100644
--- a/.mailmap
+++ b/.mailmap
@@ -538,6 +538,8 @@
 Serge Martin <edb+mesa@sigluy.net> Serge Martin (EdB) <edb+mesa@sigluy.net>
 Serge Martin <edb+mesa@sigluy.net> EdB <edb+mesa@sigluy.net>
 
+Sergii Romantsov <sergii.romantsov@globallogic.com> <sergii.romantsov@gmail.com>
+
 Sinclair Yeh <syeh@vmware.com> <sinclair.yeh@intel.com>
 
 Stefan Brüns <stefan.bruens@rwth-aachen.de> <Stefan.Bruens@rwth-aachen.de>