[Checkins] [zopefoundation/ZODB] 313702: Relax assertion in check_tid_ordering_w_commit test

[Julien Muchembled]

  Branch: refs/heads/fixup-pr307
  Home:   https://github.com/zopefoundation/ZODB
  Commit: 313702023f01623520f510c87dbaad50e7586cc2
      https://github.com/zopefoundation/ZODB/commit/313702023f01623520f510c87dbaad50e7586cc2
  Author: Julien Muchembled <jm at nexedi.com>
  Date:   2020-08-19 (Wed, 19 Aug 2020)

  Changed paths:
    M src/ZODB/tests/BasicStorage.py

  Log Message:
  -----------
  Relax assertion in check_tid_ordering_w_commit test

It is pointless for lastTransaction() to block until it is allowed to
return the TID of a transaction that has just been committed, because
it may still not be the real last TID (e.g. for some storage
implementations, invalidations are received from a shared server
via the network). While invalidations are still being processed,
it's fine to return immediately with the previous last TID.

This was clarified in commit 4a6b0283f61427c7a2d8086a271bcdfb1cb53593
("mvccadapter: check if the last TID changed without invalidation").

See pull request #316