[Flow202][keyserver][skip-ci] [3/x] Address type errors in validateCandidateMembers
Summary:
Separating this out into its own diff because I made some more opinionated changes here.
NOTE: CI will fail on this diff. I considered the possibility of fixing Flow errors BEFORE upgrading Flow, but it wasn't possible... in some cases, the fixes to support the new version of Flow caused errors in the old version. I could have hidden these type errors with $FlowFixMe lines and then later revert those, but that seemed like too much busy work.
Depends on D9850
Test Plan: Confirm the Flow errors go away
Reviewers: tomek
Reviewed By: tomek
Differential Revision: https://phab.comm.dev/D9851