bsd-family-tree: Add FreeBSD 12.3

FreeBSD 12.3 wasn't added when it was released. Add it now.

Sponsored by: Netflix
Approved by: re@ (delphij@)

(cherry picked from commit 58e6bbc5acb2d8c623cfbec37bfdda8b03d15a1f)
(cherry picked from commit af0b54d42aab4085966ce17259650105ca075979)