[FX] fix Graph python_code return type annotation (#49931)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/49931
This fixes #49932. The `maybe_return_annotation` was not being passed by reference, so it was never getting modified.
Test Plan: Imported from OSS
Reviewed By: jamesr66a
Differential Revision: D25725582
Pulled By: esqu1
fbshipit-source-id: 4136ff169a269d6b98f0b8e14d95d19e7c7cfa71
