Forwarded request #1160079 from mcalabkova

- Update to 6.0.0
* Drop support for Python 2.7, 3.5, 3.6.
* Add support for Python 3.12.
* Switch to using async/await directly instead of @coroutine/yield.
* Drop experimental support for credentials object: the corresponding
ClientStorage.__init__ parameter credentials is retained but ignored.
From now on ZEO supports authentication only via SSL certificates.
* Ensure test compatibility with both ZODB<6 and ZODB>=6 by looking for
ZODB inherited tests with prefixes check (used by ZODB<6) and test
(used by ZODB>=6)
- Drop merged patches:
* python-ZEO-no-mock.patch
* python-ZEO-no-six.patch
- Add patch skip-PackUndoLog.patch to skip test causing an error
* https://github.com/zopefoundation/ZEO/issues/240