pyrevisionstore: suppress warning of unused parameter

Summary:
The `known` parameter can't be renamed to `_known`, as the Python bindings
expect it to have the name `known`, however we can suppress the warning by
assigning it to a local variable named `_known`.  The compiler will optimize
this away.

Reviewed By: quark-zju

Differential Revision: D13239755

fbshipit-source-id: cc83be0441415dc3dd5959632dcab2af54d11513

hgext/extlib/pyrevisionstore/src/pyext.rs

@@ -156,6 +156,7 @@ py_class!(class historypack |py| {
     }
 
     def getancestors(&self, name: &PyBytes, node: &PyBytes, known: Option<&PyObject>) -> PyResult<PyDict> {
+        let _known = known;
         <HistoryStorePyExt>::get_ancestors(self.store(py).as_ref(), py, name, node)
     }