[github-actions] Pin dependencies

[renovate]

This PR contains the following updates:

Package	Type	Update	Change
actions/checkout	action	pinDigest	→ df4cb1c
actions/setup-python	action	pinDigest	→ a309ff8
codecov/codecov-action	action	pinDigest	→ fb8b358

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Configuration

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (b668f48) to head (37068c6).

Additional details and impacted files

@@            Coverage Diff            @@
##            master       #15   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          130       130           
  Branches        13        13           
=========================================
  Hits           130       130           

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