Update setup-python action to v6

[mcbarton]

Description

Please include a summary of changes, motivation and context for this PR.

Fixes # (issue)

Type of change

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• Bug fix
• New feature
• Added/removed dependencies
• Required documentation updates

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.78%. Comparing base (4449bfb) to head (8360009).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #377   +/-   ##
=======================================
  Coverage   81.78%   81.78%           
=======================================
  Files          20       20           
  Lines         950      950           
  Branches       87       87           
=======================================
  Hits          777      777           
  Misses        173      173           

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