* gnu/packages/python-xyz.scm (python-isort): Update to 5.7.0.
[source]: Delete checked in binary wheels in a snippet.
[arguments]: New field.
[phases]: Replace the build and install phases, implementing the basics of a
PEP 517 build system.
{check}: Override phase.
{install-example-plugins}: New phase.
[native-inputs]: Remove python-mock. Add git-minimal, python-black,
python-colorama, python-hypothesmith, python-libcst-minimal,
python-poetry-core, python-pylama, python-pypa-build and python-pytest-mock.
[home-page]: Update home page.
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