[keyserver] Fix fetchKnownUserInfos

Summary:
More context in Linear issue. This diff fixes an issue introduced in D4530.

In that diff I reordered the UNION SELECT list without reordering the SELECT list. Oops!

Test Plan: This time I definitely tested both MySQL 5.7 and MariaDB 10.8 and made sure that ENG-1409 is resolved on both

Reviewers: def-au1t, atul, palys-swm

Reviewed By: atul

Subscribers: Adrian, yayabosh

Differential Revision: https://phab.comm.dev/D4558