tests: use https:// scheme in webtest client (#71948)

Adaptation to change in authentic settings (SESSION_COOKIE_SECURE=True).

tests/conftest.py

@@ -25,7 +25,7 @@ def app(request, db, settings, tmpdir):
     request.addfinalizer(wtm._unpatch_settings)
     settings.MEDIA_DIR = str(tmpdir.mkdir('media'))
     call_command('loaddata', 'cut_attributes.json')
-    return django_webtest.DjangoTestApp(extra_environ={'HTTP_HOST': 'localhost'})
+    return django_webtest.DjangoTestApp(extra_environ={'HTTP_HOST': 'localhost', 'wsgi.url_scheme': 'https'})
 
 
 @pytest.fixture