fix python build break

Signed-off-by: Nikolaj Bjorner <nbjorner@microsoft.com>

src/api/python/z3/z3.py

@@ -4298,7 +4298,7 @@ def is_array(a):
     return isinstance(a, ArrayRef)
 
 def is_array_sort(a):
-    return _ast_kind(a.ctx(), a.sort()) == Z3_ARRAY_SORT
+    return _ast_kind(a.ctx, a.sort()) == Z3_ARRAY_SORT
 
 def is_const_array(a):
     """Return `True` if `a` is a Z3 constant array.