Mark unauthenticated user for translation in Audit Event

ee/changelogs/unreleased/sk-212258-add-translated-text.yml

+---
+title: Translate unauthenticated user string for Audit Event
+merge_request:
+author: Sashi Kumar
+type: other

ee/lib/gitlab/audit/unauthenticated_author.rb

@@ -7,10 +7,10 @@ module Gitlab
         super(id: -1, name: name)
       end
 
-      # Events that are authored by unathenticated users, should be
+      # Events that are authored by unauthenticated users, should be
       # shown as authored by `An unauthenticated user` in the UI.
       def name
-        @name || 'An unauthenticated user'
+        @name || _('An unauthenticated user')
       end
     end
   end

locale/gitlab.pot

@@ -2293,6 +2293,9 @@ msgstr ""
 msgid "An issue can be a bug, a todo or a feature request that needs to be discussed in a project. Besides, issues are searchable and filterable."
 msgstr ""
 
+msgid "An unauthenticated user"
+msgstr ""
+
 msgid "An unexpected error occurred while checking the project environment."
 msgstr ""