Add myself to .mailmap

See https://github.com/nextcloud/server/pull/20241

.mailmap

@@ -380,6 +380,7 @@ tbelau666 <thomas.belau@gmx.de>
 TheSFReader <TheSFReader@gmail.com>
 Thibaut GRIDEL <tgridel@free.fr>
 thomas <thomas@thomas-VirtualBox.(none)>
+Thomas Citharel <nextcloud@tcit.fr> Thomas Citharel <tcit@tcit.fr>
 Thomas Müller <thomas.mueller@tmit.eu> Thomas Mueller <thomas.mueller@tmit.eu>
 Thomas Müller <thomas.mueller@tmit.eu> Thomas Müller <DeepDiver1975@users.noreply.github.com>
 Thomas Olsen <tol@tanghus>