docs: update stale commands for running local tests in TESTING.md

[stephensp]

These commands no longer point to valid paths.

• Have you followed the guidelines for contributing?
• Have you signed the CLA?
• Have you successfully run make lint?
• Have you successfully run pytest tests/unit?

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[mr-cal]

Thanks!

[codecov-commenter]

Codecov Report

Merging #4428 (aca367c) into main (f6bbea5) will decrease coverage by 0.02%.
The diff coverage is n/a.

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@@            Coverage Diff             @@
##             main    #4428      +/-   ##
==========================================
- Coverage   89.20%   89.18%   -0.02%     
==========================================
  Files         322      321       -1     
  Lines       21663    21614      -49     
==========================================
- Hits        19324    19277      -47     
+ Misses       2339     2337       -2     

see 5 files with indirect coverage changes

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