CI got broken by the termwiz release. This commit teaches the
various `git describe --tags` calls to filter to the wezterm
tags which all start with the year. We're match `20*` which should
be good for the next 79 years.
I've removed the vergen dependency as there was no way to teach it
to do the equivalent matching, and it wasn't a terrible burden
to just inline the git describe call anyway.