Decrease PostgreSQL version on FreeBSD to 13

Summary:
Version 14 is still beta, and pull v13 packages currently.

This is a follow-up for 5fe5ee9e.

Test Plan: Test D2393 on FreeBSD (e.g. WindRiver)

Reviewers: dereckson

Reviewed By: dereckson

Differential Revision: https://devcentral.nasqueron.org/D2408