Fix missing initializer for Python 3.13

Building with Python 3.13 on Linux with GCC 11 yields following warning:

  In constructor ‘lass::python::impl::ClassDefinition::ClassDefinition(const char*, const char*, Py_ssize_t, richcmpfunc, lass::python::impl::ClassDefinition*, lass::python::impl::ClassDefinition::TClassRegisterHook)’:
  lass/lass/python/class_definition.cpp:168:9: warning: missing initializer for member ‘_typeobject::tp_versions_used’ [-Wmissing-field-initializers]

lass/python/class_definition.cpp

@@ -164,6 +164,9 @@ ClassDefinition::ClassDefinition(
 #endif
 #if PY_VERSION_HEX >= 0x030C0000 // >= 3.12
 		0,	/*tp_watched, internal only */
+#endif
+#if PY_VERSION_HEX >= 0x030D0000 // >= 3.13
+		0,	/*tp_versions_used */
 #endif
 	};
 	type_ = type;