tests/conftest: Fix errors after swh-indexer API update
See https://jenkins.softwareheritage.org/job/DENV/job/tests/295/artifact/swh-web.log
While a new tag is not created for swh-indexer, we have to use the deprecated policy_update
parameter or tests will fail when using tox
.
Migrated from D4439 (view on Phabricator)