Issue #16012: Fix a regression in pyexpat. The parser's UseForeignDTD()
method doesn't require an argument again.
diff --git a/Modules/pyexpat.c b/Modules/pyexpat.c
index 4d9a1e5..f269113 100644
--- a/Modules/pyexpat.c
+++ b/Modules/pyexpat.c
@@ -1176,7 +1176,7 @@
     PyObject *flagobj = NULL;
     int flag = 1;
     enum XML_Error rc;
-    if (!PyArg_ParseTuple(args, "O:UseForeignDTD", &flagobj))
+    if (!PyArg_ParseTuple(args, "|O:UseForeignDTD", &flagobj))
         return NULL;
     if (flagobj != NULL) {
         flag = PyObject_IsTrue(flagobj);