fix up to sync internal/oss (#7843)

fix up to main

Author: lucylq

extension/flat_tensor/serialize/flat_tensor_schema.py

@@ -4,6 +4,7 @@
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
 
+# pyre-strict
 
 from dataclasses import dataclass
 from typing import List