Add rancher provisioning tests

[manno]

Extend the existing workflow to also run the provisioning tests.

• find a new name for the workflow, a name that contains "test" as a verb so we can watch out for daily failures and run it on demand, Release Fleet against test Rancher charts repo -> Test Built Fleet Chart in Rancher (???)
• the tests actually succeed in our CI, unlike https://github.com/rancher/fleet/actions/runs/13809662927
• note that this involves two workflows, the chart release workflow uses the test workflow

Initial attempt to implement this quickly: #3439