Change `series` to `base`

[chanchiwai-ray]

With jubilant, series defined in the integration test workflow will not be useful because jubilant.Juju.deploy take base instead.

[syncronize-issues-to-jira]

Thank you for reporting your feedback to us!

The internal ticket has been created: https://warthogs.atlassian.net/browse/ISD-4848.

This message was autogenerated