fixing typo (#25714)

Co-authored-by: Tom De Moor <tom@controlaltdieliet.be>

server/i18n/en.json

@@ -8900,7 +8900,7 @@
   },
   {
     "id": "model.config.is_valid.message_export.global_relay.customer_type.app_error",
-    "translation": "Message export GlobalRelaySettings.CustomerType must be set to one of either 'A9', 'A10' or 'CUSTOM."
+    "translation": "Message export GlobalRelaySettings.CustomerType must be set to one of either 'A9', 'A10' or 'CUSTOM'."
   },
   {
     "id": "model.config.is_valid.message_export.global_relay.customer_type_custom.app_error",