[CHANGE] Update Codecov token to environment variable in workflow

[ppfeufer]

Description

Change

• Provide codecov token environment variable in workflow ([v4] Error: Codecov token not found in a PR from a fork to a pubilc repo codecov/codecov-action#1292)

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality not to work as expected)

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented on my code, particularly in hard-to-understand areas
• I have checked my code and corrected any misspellings

[codecov]

Codecov Report

Merging #112 (08476b5) into master (d4855b1) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #112   +/-   ##
=======================================
  Coverage   97.37%   97.37%           
=======================================
  Files          10       10           
  Lines         228      228           
  Branches       12       12           
=======================================
  Hits          222      222           
  Misses          3        3           
  Partials        3        3           

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