Update .mailmap to promote my livename

I had apparently forgotten to update the Rust mailmap file for my previous commits!

Author: Amanda Stjerna

.mailmap

@@ -31,6 +31,8 @@ Alexis Beingessner <a.beingessner@gmail.com>
 Alfie John <alfie@alfie.wtf> Alfie John <alfiej@fastmail.fm>
 Alona Enraght-Moony <code@alona.page> <nixon.emoony@gmail.com>
 Alona Enraght-Moony <code@alona.page> <nixon@caminus.local>
+Amanda Stjerna <mail@amandastjerna.se> <albin.stjerna@gmail.com>
+Amanda Stjerna <mail@amandastjerna.se> <amanda.stjerna@it.uu.se>
 Amos Onn <amosonn@gmail.com>
 Ana-Maria Mihalache <mihalacheana.maria@yahoo.com>
 Anatoly Ikorsky <aikorsky@gmail.com>