update-check inherit type

[nekopsykose]

currently we detect some some special hosts in expand_source, e.g. codeberg, gitlab

for the latter two (and technically also pagure, srht, ... but almost nobody hosts those), it would be nice if there was some way to basically just do

# in update.py
inherit = "codeberg" # or maybe gitea, or forgejo, whatever name

since every self-hosted version of those has the same kind of lookup but fails autodetection since the url= doesn't match

though since the update.py would have to be made anyway this only saves a few characters really