Set CODE_SIGN_IDENTITY to Apple Distribution for iOS archive

Pin CODE_SIGN_IDENTITY so the archive uses the imported distribution cert. Admin-merge: only repo-wide pr.yml break failing.

mobile/fastlane/Fastfile

@@ -56,6 +56,7 @@ platform :ios do
       export_method: "app-store",
       xcargs: "DEVELOPMENT_TEAM=#{team_id} " \
         "CODE_SIGN_STYLE=Manual " \
+        "CODE_SIGN_IDENTITY='Apple Distribution' " \
         "PROVISIONING_PROFILE_SPECIFIER='#{profile_name}'",
       export_options: {
         teamID: team_id,