fix: properly mark the C extension as safe for free-threading. #1799

https://github.com/python/cpython/blob/main/Doc/howto/free-threading-extensions.rst#c-api-extension-support-for-free-threading

GitOrigin-RevId: b18485e3ac15b5d5b7be8d7117fef9994b745bf8
Change-Id: I80d4a80d6dd07e42797a3ebd65969e6c5a743f49
2 files changed