Add codecov token to CI

[gdalle]

Fix #303

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.16%. Comparing base (1365d5e) to head (58aaed4).
Report is 10 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master     #305       +/-   ##
===========================================
+ Coverage    0.06%   83.16%   +83.09%     
===========================================
  Files          25       25               
  Lines        1463     1491       +28     
===========================================
+ Hits            1     1240     +1239     
+ Misses       1462      251     -1211     

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