Make test_no_wait_call more robust

[dimaqq]

AssertionError: assert "Implicitly c...ss-qurgf63h'>" == 'ExecProcess ...wait_output()'
  - ExecProcess instance garbage collected without call to wait() or wait_output()
  + Implicitly cleaning up <TemporaryDirectory '/tmp/ops-harness-qurgf63h'>

https://github.com/canonical/operator/actions/runs/13061947820/job/36446760834

[dimaqq]

May be a transient failure, as 3.10 tripped but other versions didn't.