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* Fix device verification to return the device used to sign the
challenge instead of the device used to initiate the challenge.
* Switch to setuptools_scm for automatic git versioning.
* Move package data to setup.cfg.
* Switch django TestCase to pytest fixtures.
* Add Python 3.9 and Django 3.2 to the support matrix.
* Move test dependencies to the otp_u2f[test] extra.
* Switch to PEP517 package builder.
* Exclude tests from package.