pytest.ini: Avoid loading django plugin to prevent fixture name clash

pytest-django and pytest-flask both declare a fixture named client and the wrong one may be picked when running swh-scanner tests.

So avoid the loading of pytest django plugin to prevent errors when running tests.

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Migrated from D3052 (view on Phabricator)

pytest.ini

 [pytest]
+addopts = -p no:django
 norecursedirs = docs
 addopts = --live-server-port 6600 -p no:django --no-live-server-clean-stop