.testing: Codecov token for unit test upload

[marshallward]

The codecov token was added to the tc* test upload, but not the unit test upload. This patch adds the token to the unit testing.

[codecov]

Codecov Report

Merging #497 (b569e12) into dev/gfdl (3650339) will increase coverage by 0.00%.
The diff coverage is n/a.

❗ Current head b569e12 differs from pull request most recent head c470ce9. Consider uploading reports for the commit c470ce9 to get more accurate results

@@            Coverage Diff            @@
##           dev/gfdl     #497   +/-   ##
=========================================
  Coverage     37.82%   37.83%           
=========================================
  Files           270      270           
  Lines         78340    78340           
  Branches      14503    14503           
=========================================
+ Hits          29636    29637    +1     
+ Misses        43300    43298    -2     
- Partials       5404     5405    +1     

see 1 file with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[marshallward]

Gaea regression: https://gitlab.gfdl.noaa.gov/ogrp/MOM6/-/pipelines/20859 ✔️