Python: Improve docstring and make predicate private

Author: tausbn

python/ql/lib/semmle/python/dataflow/new/internal/DataFlowDispatch.qll

@@ -308,9 +308,12 @@ predicate hasContextmanagerDecorator(Function func) {
  * Holds if the function `func` has a `typing.overload` decorator.
  * Such functions are type stubs that declare an overload signature but are
  * not the actual implementation.
+ *
+ * Normally we would want to model this using API graphs for more precision, but since this
+ * predicate is used in the call graph computation, we have to use a more syntactic approach.
  */
 overlay[local]
-predicate hasOverloadDecorator(Function func) {
+private predicate hasOverloadDecorator(Function func) {
   exists(ControlFlowNode overload |
     overload.(NameNode).getId() = "overload" and overload.(NameNode).isGlobal()
     or