test_client: Migrate multisteps_deposit scenario to use requests_mock_datadir
Instead of mock.
Note that right now, we should be using requests_mock_datadir_visits so we can leverage a second visit with the correct status. But this refused to work so far. A FIXME has been added to deal with this soon.
Test Plan
tox
Migrated from D4213 (view on Phabricator)