Update CI config

[fingolfin]

To keep code coverage working, you'll have to define a CODECOV_TOKEN.
This can be done once in the peal GitHub org for all repositories
in it at once.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.43%. Comparing base (e85cf28) to head (09dd840).
Report is 11 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master       #9      +/-   ##
==========================================
- Coverage   92.90%   92.43%   -0.48%     
==========================================
  Files          10       12       +2     
  Lines         550      542       -8     
==========================================
- Hits          511      501      -10     
- Misses         39       41       +2     

see 4 files with indirect coverage changes

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