Ensure codecov token is used

[michaelsproul]

Fix failing cargo-tarpaulin CI.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 49.27%. Comparing base (b6b5ff2) to head (4ac5f24).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #11      +/-   ##
==========================================
- Coverage   52.17%   49.27%   -2.90%     
==========================================
  Files           1        2       +1     
  Lines          69       69              
==========================================
- Hits           36       34       -2     
- Misses         33       35       +2     

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