[landing] Fix ConnectFarcaster

Summary: Addresses ENG-9506. @horsefacts helped me out here. We should be waiting for connect to finish before calling signIn.

Test Plan: I tested the SIWF flow on Android following this doc

Reviewers: varun, will

Reviewed By: varun

Subscribers: tomek

Differential Revision: https://phab.comm.dev/D13620