meta: consolidate AUTHORS information for geirha

Use a .mailmap entry to consolidate the two entries for gierha in
AUTHORS into a single entry.

PR-URL: #40406
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>

.mailmap

@@ -151,6 +151,7 @@ Gabriel de Perthuis <g2p.code@gmail.com>
 Gareth Ellis <gareth.ellis@uk.ibm.com> <gareth@gsellis.com>
 Garwah Lam <garwahlam@gmail.com>
 garygsc <garygsc@gmail.com> <GaryGSC@users.noreply.github.com>
+Geir Hauge <geir.hauge@gmail.com> <geir.hauge@ntnu.no>
 Geoffrey Booth <webadmin@geoffreybooth.com> <GeoffreyBooth@users.noreply.github.com>
 Geoffrey Booth <webadmin@geoffreybooth.com> <webmaster@geoffreybooth.com>
 Geoffrey Bugaisky <gbugaisk@gmail.com>

AUTHORS

@@ -551,7 +551,7 @@ Yuki KAN <re@pixely.jp>
 Evan Carroll <me@evancarroll.com>
 William Bert <william@spanishdict.com>
 goussardg <guillaume.goussard@mgo.com>
-Geir Hauge <geir.hauge@ntnu.no>
+Geir Hauge <geir.hauge@gmail.com>
 Farrin Reid <blakmatrix@gmail.com>
 Denys Zariaiev <denys.zariaiev@gmail.com>
 Sean McArthur <sean.monstar@gmail.com>
@@ -2664,7 +2664,6 @@ Avi ד <avi.the.coder@gmail.com>
 Thomas <hakerh403@gmail.com>
 Aymen Naghmouchi <aymen.aymen@live.it>
 himself65 <himself65@outlook.com>
-Geir Hauge <geir.hauge@gmail.com>
 Patrick Gansterer <paroga@paroga.com>
 Nicolas Moteau <nicolas.moteau@orange.com>
 Anthony Tuininga <anthony.tuininga@oracle.com>