Since there is no generic information in `flag_value.__init__()`,
`flag_value` descriptors get stored as `flag_value[<nothing>]` in mypy
strict mode and then the `__get__` overloads never match. This leads to
errors when using things like `permissions_instance.embed_links` since
`<nothing>` never matches `Permissions`.
The generic inheritance isn't needed at all since the type information
we care about comes from the call site of `__get__` and not the
instantiation of the descriptor.
Bryan ForbesandGitHub
