.mailmap: add a few aliases for Christoph Haag

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/1999>
diff --git a/.mailmap b/.mailmap
index 284a25f..81db771 100644
--- a/.mailmap
+++ b/.mailmap
@@ -137,6 +137,10 @@
 
 Christoph Bumiller <christoph.bumiller@speed.at> <e0425955@student.tuwien.ac.at>
 
+Christoph Haag <haagch@frickel.club> <christoph.haag@collabora.com>
+Christoph Haag <haagch@frickel.club> <haagch+mesa@frickel.club>
+Christoph Haag <haagch@frickel.club> <haagch+mesadev@frickel.club>
+
 Christopher James Halse Rogers <christopher.halse.rogers@canonical.com> Christopher James Halse Rogers <raof@ubuntu.com>
 
 Claudio Ciccani <klan@directfb.org> <klan@users.sf.net>