devel/py-zclockfile: Update to 2.0

• Add a "do-test" target to make future QA easier while I'm here.

Changelog:

https://github.com/zopefoundation/zc.lockfile/blob/2.0/CHANGES.rst

PR: 247891
Approved by: maintainer timeout (14+ days)
MFH: No (contains API incompatible changes)