Fix ownership for end method in StartedTestRun

[njordr]

Fix the end method that takes ownership of self without any needs

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 99.5%. Comparing base (081cd2d) to head (07591a7).

Additional details and impacted files

[mimir-d]

takes ownership of self without any needs

this is incorrect; the "need" is semantic. All these end methods (in StartedTestRun, StartedTestStep) consume self in order to make it impossible to output new messages after the test run/step has ended.

in the example https://github.com/opencomputeproject/ocp-diag-core-rust/blob/dev/examples/simple_no_scopes.rs#L27, it makes it such that writing something like step.add_diagnosis() after line 27 would not compile.