fix: expect 'DocumentSnapshot.__hash__' to expect 'DatetimeWithNanosecons'

[Arushi201296]

Fixes #391 🦕

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[google-cla]

Thanks for your pull request. It looks like this may be your first contribution to a Google open source project (if not, look below for help). Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

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[tseaver]

Thanks very much for the patch! The PR needs to make corresponding changes to the unit test(s) for __hash__, found in tests/unit/v1/test_base_document.py.

You can run the tests locally with nox: install it via pip install nox and then run nox -s unit-3.8.

[tseaver]

Tagged as do not merge pending resolution of the discussion in #398.

[crwilcox]

Note that there are current test failures to address

[tseaver]

@Arushi201296 I've added the needed test in #467, and so I'm closing this PR. Again, thanks for the report and the patch!