[jOOQ/jOOQ#18865] Fix regression

While N_CURRENT_TIME is a DSL::systemName, it appears that in some test scenarios, we're quoting the name to system_time, e.g. in SQLite, which produces wrong results.

jOOQ/src/main/java/org/jooq/impl/CurrentTime.java

@@ -114,7 +114,7 @@ final class CurrentTime<T> extends AbstractField<T> implements QOM.CurrentTime<T
                 break;
 
             default:
-                ctx.visit(N_CURRENT_TIME);
+                ctx.visit(K_CURRENT).sql('_').visit(K_TIME);
                 break;
         }
     }