Fix permission errors w/ readonly tmpdirs and pytest 7.3

[IAlibay]

Azure pipelines has been failing recently (see #4121 ), due to the latest pytest 7.3 release.

The source of the error seems to be a mixture of windows, python 3.9, pytest and pathlib incompatibilities when trying to clean up temporary directories that have been set to read-only.

To fix this, here we just conclude the one affected test by re-enabling write permissions to the directory and removing it ahead of the test completing.

PR Checklist

• Tests?
• Docs?
• CHANGELOG updated?
• Issue raised/referenced?

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📚 Documentation preview 📚: https://readthedocs-preview--4122.org.readthedocs.build/en/4122/

[github-actions]

Linter Bot Results:

Hi @IAlibay! Thanks for making this PR. We linted your code and found the following:

Some issues were found with the formatting of your code.

Code Location	Outcome
main package	✅ Passed
testsuite	⚠️ Possible failure

Please have a look at the darker-main-code and darker-test-code steps here for more details: https://github.com/MDAnalysis/mdanalysis/actions/runs/4652406475/jobs/8232597712

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Please note: The black linter is purely informational, you can safely ignore these outcomes if there are no flake8 failures!

[codecov]

Codecov Report

Patch coverage has no change and project coverage change: +0.01 🎉

Comparison is base (a440165) 93.58% compared to head (7bed9f4) 93.59%.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #4122      +/-   ##
===========================================
+ Coverage    93.58%   93.59%   +0.01%     
===========================================
  Files          192      192              
  Lines        25134    25134              
  Branches      4056     4056              
===========================================
+ Hits         23521    23524       +3     
+ Misses        1094     1092       -2     
+ Partials       519      518       -1     

see 1 file with indirect coverage changes

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[IAlibay]

@MDAnalysis/coredevs this will need to take priority for merging so that we can get CI working again.

[orbeckst]

ugly but ok, please see comment.

Happy Easter!