Flatten tests/rest/client/{v1,v2_alpha} too (#10667)

changelog.d/10667.misc

mypy.ini

tests/rest/client/test_account.py

tests/rest/client/test_auth.py

tests/rest/client/test_capabilities.py

tests/rest/client/test_directory.py

tests/rest/client/test_events.py

tests/rest/client/test_filter.py

tests/rest/client/test_keys.py

tests/rest/client/test_login.py

tests/rest/client/test_password_policy.py

tests/rest/client/test_presence.py

tests/rest/client/test_profile.py

tests/rest/client/test_push_rule_attrs.py

tests/rest/client/test_register.py

tests/rest/client/test_relations.py

tests/rest/client/test_report_event.py

tests/rest/client/test_rooms.py

tests/rest/client/test_sendtodevice.py

tests/rest/client/test_shared_rooms.py