fix: account for Windows in code and tests

[mkniewallner]

PR Checklist

• A description of the changes is added to the description of this PR.
• If there is a related issue, make sure it is linked to this PR.
• If you've fixed a bug or added code that should be tested, add tests!
• Documentation in docs is updated

Description of changes

This PR enables #342 by fixing a few issues spotted when trying to add the CI on Windows.

mkniewallner#23 shows that Windows jobs are green when including the fixes from this PR.

[codecov]

Codecov Report

Merging #343 (1e47f3f) into main (2471494) will not change coverage.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #343   +/-   ##
=====================================
  Coverage   95.9%   95.9%           
=====================================
  Files         29      29           
  Lines        915     915           
  Branches     185     185           
=====================================
  Hits         878     878           
  Misses        24      24           
  Partials      13      13           

Impacted Files	Coverage Δ
deptry/python_file_finder.py	100.0% <ø> (ø)
...ry/imports/extractors/notebook_import_extractor.py	87.8% <100.0%> (ø)
...ptry/imports/extractors/python_import_extractor.py	100.0% <100.0%> (ø)

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