unknown flavor py37

From: Daniel Braniss <danny_at_cs.huji.ac.il>
Date: Thu, 26 May 2022 14:10:00 UTC
im using portmaster.

after a resent update to /usr/ports, the default python became 3.8, fine by me, but I still want to
keep 3,7.
some Makefiles require 3,8+, again no problem.
but some have 3.6+, and make FLAVOR=37 failes with unknown flavor …

any work around?