chore(ci): fix code coverage uploads

[mccutchen]

Looks like codecov.io now requires an explicit auth token, per this failed upload:

[2024-09-13T21:34:57.324Z] ['error'] There was an error running the uploader: Error uploading to https://codecov.io: Error: There was an error fetching the storage URL during POST: 429 - {'detail': ErrorDetail(string='Rate limit reached. Please upload with the Codecov repository upload token to resolve issue. Expected time to availability: 1478s.', code='throttled')}
[2024-09-13T21:34:57.324Z] ['info'] Codecov will exit with status code 0. If you are expecting a non-zero exit code, please pass in the -Z flag

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.86%. Comparing base (8f905de) to head (98a27fe).
Report is 5 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #183      +/-   ##
==========================================
- Coverage   95.04%   94.86%   -0.18%     
==========================================
  Files          10       10              
  Lines        2179     1714     -465     
==========================================
- Hits         2071     1626     -445     
+ Misses         74       50      -24     
- Partials       34       38       +4     

see 8 files with indirect coverage changes