Small fix type hints in mobile optimizer (#59282)
Summary:
Adjusts type hints for optimize_for_mobile to be consistent with the default. Right now using optimize_for_mobile and only passing a script_module gives me a type error complaining about preserved_methods can't be None.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/59282
Test Plan:
Imported from GitHub, without a `Test Plan:` line.
Open source tests ran the lints. Internal CI should be enough here.
Reviewed By: jbschlosser
Differential Revision: D28838159
Pulled By: JacobSzwejbka
fbshipit-source-id: dd1e9aff00a759f71d32025d8c5b01e612c869a5
