fix: type Finch.request_opt() was missing the :request_timeout option

[Mayeu]

Hello 👋

First, thank you for your work on Finch 🙏

We encountered the following dyalixir error in our code:

lib/app/rpc.ex:352:no_return
Function post/2 has no local return.

Our function was only calling Finch.build(...) |> Finch.resquest(...) so nothing that could have raised. In this end, this was triggered because the :request_timeout keyword was missing from the Finch.request_opt() type.

[Mayeu]

I forced push to fix the linting error the CI reported.

[sneako]

Thank you!!