MM-68702: Reject demoting bot accounts to guest (#36487) (#36634)

Automatic Merge

server/i18n/en.json

@@ -4130,6 +4130,10 @@
     "id": "api.user.demote_user_to_guest.already_guest.app_error",
     "translation": "Unable to convert the user to guest because is already a guest."
   },
+  {
+    "id": "api.user.demote_user_to_guest.bot_not_allowed.app_error",
+    "translation": "Bot accounts cannot be converted to guest accounts."
+  },
   {
     "id": "api.user.email_to_ldap.not_available.app_error",
     "translation": "AD/LDAP not available on this server."