Always reset pytest working directory to invocation dir

[timothy-nunn]

Getting the cwd within the return_to_root fixture was prone to error when another fixture ran first and changed the working directory. I have set the fixture now to return the working directory to the invocation directory (where the user called pytest from).

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 48.83%. Comparing base (a68bb7f) to head (bea4193).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4384      +/-   ##
==========================================
- Coverage   48.84%   48.83%   -0.01%     
==========================================
  Files         151      151              
  Lines       29360    29376      +16     
==========================================
+ Hits        14340    14347       +7     
- Misses      15020    15029       +9     

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