.mailmap: add an alias for Daniel Schürmann

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index 4e55df0..edb418d 100644
--- a/.mailmap
+++ b/.mailmap
@@ -160,6 +160,8 @@
 
 Craig Stout <cstout@google.com>
 
+Daniel Schürmann <daniel.schuermann@campus.tu-berlin.de> <daniel@schuermann.dev>
+
 Daniel Skinner <sio@users.sourceforge.net> sio <sio>
 
 Daniel Stone <daniels@collabora.com> <daniel@fooishbar.org>