3.8 was previously used, but it's not available in the
currently used Docker image.

…cp/templates/python_library/.kokoro (#849)

Source-Link: googleapis/synthtool@b4fe62e
Post-Processor: gcr.io/cloud-devrel-public-resources/owlbot-python:latest@sha256:3bf87e47c2173d7eed42714589dc4da2c07c3268610f1e47f8e1a30decbfc7f1

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Different Zlib compression levels produce different
compression markers.

Co-authored-by: Zhou Wang <wangzhou@google.com>

Co-authored-by: Zhou Wang <wangzhou@google.com>

Currently, NDB clients do not recognize client_options as a keyword argument.
Furthermore, because they currently create a Datastore channel directly,
we have to manually modify the host to ensure it is passed to the Datastore
channel. Merely setting the API endpoint via environment variable is not
sufficient, because that variable's presence is currently used to test
whether or not we are using the datastore emulator.

Bump api-core dep to ensure we have the necessary API support,
also sync it up with google-cloud-datastore.

This is available in unittest for Py3. We only
needed to do this for Python 2, which is no longer
supported.

Co-authored-by: Anthonios Partheniou <partheniou@google.com>

Mostly get rid of older Py2-only code

Co-authored-by: release-please[bot] <55107282+release-please[bot]@users.noreply.github.com>