Fix crash on interactive cleanup twice

[dfsp-spirit]

Changes Summary

• insta-fix for a bug discovered by DJ: on the latest dev, running spy.cleanup(interactive=False) twice in a row crashes Syncopy., #516
• cannot easily add tests for the bug to verify that it is fixed: running spy.cleanup while other tests are run in parallel may remove their temp files, and thus make other tests fail at random.

Reviewer Checklist

• [ ] Are testing routines present?
• [ ] Do objects in the global package namespace perform proper parsing of their input?
• [ ] Are all docstrings complete and accurate?
• [ ] Is the CHANGELOG.md up to date?

[codecov[bot]]

Codecov Report

Patch coverage: 75.00% and project coverage change: -0.05 :warning:

Comparison is base (6cd294d) 69.04% compared to head (78d3bcc) 69.00%.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## dev #515 +/- ## ========================================== - Coverage 69.04% 69.00% -0.05% ========================================== Files 87 87 Lines 10164 10169 +5 Branches 2072 2072 ========================================== - Hits 7018 7017 -1 - Misses 2612 2616 +4 - Partials 534 536 +2 ``` | [Impacted Files](https://app.codecov.io/gh/esi-neuroscience/syncopy/pull/515?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esi-neuroscience) | Coverage Δ | | |---|---|---| | [syncopy/shared/errors.py](https://app.codecov.io/gh/esi-neuroscience/syncopy/pull/515?src=pr&el=tree&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esi-neuroscience#diff-c3luY29weS9zaGFyZWQvZXJyb3JzLnB5) | `44.08% <75.00%> (+0.43%)` | :arrow_up: | ... and [2 files with indirect coverage changes](https://app.codecov.io/gh/esi-neuroscience/syncopy/pull/515/indirect-changes?src=pr&el=tree-more&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=esi-neuroscience)

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