collide: Fix typo causing compile error on Windows with Python 3.10

panda/src/collide/collisionTraverser_ext.cxx

@@ -69,7 +69,7 @@ __setstate__(PyObject *state) {
   _this->set_name(std::string(data, len));
 
   _this->set_respect_prev_transform(PyTuple_GET_ITEM(state, 1) != Py_False);
-  size_t num_colliders = (ssize_t)PyLong_AsLong(PyTuple_GET_ITEM(state, 2));
+  size_t num_colliders = (size_t)PyLong_AsLong(PyTuple_GET_ITEM(state, 2));
 
   for (size_t i = 0; i < num_colliders; ++i) {
     NodePath *collider = (NodePath *)DtoolInstance_VOID_PTR(PyTuple_GET_ITEM(state, i * 2 + 3));