Add tests for custom pybind type_casters (#89897)
This is a followup to #89115 which Fixes #88958
This adds tests to verify at runtime that the types returned by custom pybind type_casters are correctly specified in the second argument to `PYBIND11_TYPE_CASTER`.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/89897
Approved by: https://github.com/ezyang
