update coverage CI action

[orbeckst]

• added CODECOV_TOKEN to the repo secrets
• use token in workflow
• upgrade action from v2 to v3

[codecov[bot]]

Codecov Report

Merging #263 (954823c) into master (be76199) will not change coverage. The diff coverage is n/a.

@@           Coverage Diff           @@
##           master     #263   +/-   ##
=======================================
  Coverage   98.69%   98.69%           
=======================================
  Files          26       26           
  Lines        1759     1759           
  Branches      363      363           
=======================================
  Hits         1736     1736           
  Misses          3        3           
  Partials       20       20           

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