devel/git-cinnabar: unbreak with python310

$ git clone hg::https://hg.mozilla.org/projects/nss
Cloning into 'nss'...
Traceback (most recent call last):

File "/usr/local/libexec/git-core/git-remote-hg", line 9, in <module>
  from cinnabar.githg import GitHgStore
File "g/usr/local/libexec/git-core/pythonlib/cinnabar/githg.py", line 17, in <module>
  from collections import (

ImportError: cannot import name 'Sequence' from 'collections' (/usr/local/lib/python3.10/collections/__init__.py)