add missing backticks

Author: renetapopova

modules/ROOT/pages/errors/gql-errors.adoc

@@ -457,7 +457,7 @@ Status description:: error: general processing exception - invalid server state
 === 50N11
 
 
-Status description:: error: general processing exception - constraint creation failed. Unable to create { $constrDescrOrName }.
+Status description:: error: general processing exception - constraint creation failed. Unable to create `{ $constrDescrOrName }`.
 
 === 50N12