tox dependency virtualenv dropped support for creating
Python 3.6 environments in a minor release. [1]
Announce deprecation of Anymail Python 3.6 support.
Until that can take effect, pin an older version of
virtualenv that still works for tox py36 testenv.
[1]: See https://github.com/pypa/virtualenv/pull/2548#issuecomment-1527278210 et seq
pypy-3.8-v7.3.8 accidentally shipped with sqlite v3.7.17,
which is a decade old, and causes the tests to fail with
`django.core.exceptions.ImproperlyConfigured:
SQLite 3.9.0 or later is required`.
Until pypy-3.8-v7.3.9 is available in actions/setup-python,
work around the problem by forcing unqualified "pypy-3.8"
to specific (older) version "pypy-3.8-v7.3.7".
See https://foss.heptapod.net/pypy/pypy/-/issues/3690
and https://github.com/actions/setup-python/issues/339.
* Split test, integration-test, and release workflows,
simplifying config and logic for each.
* Use environment to separate secrets for release workflow.
* Update test matrix with newer Django and Python versions.
* Omit default_app_config under Django 3.2 and later
to avoid DeprecationWarning
* Also adds testing on Python 3.9, 3.10-alpha
* Also updates test matrix to include all supported
Python versions (some older Django versions expanded
Python support in patch releases)
Related changes:
* remove Travis-CI config; stop running tests on Travis
* rename live integration test environment variables
to all start with `ANYMAIL_TEST_` (simplifies tox config)
