ci: upload go-tests test results to codecov

[geoknee]

Closes #12999

I have added the relevant token to our CI environment following these instructions.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 44.24%. Comparing base (ea7f56c) to head (2b380b6).
Report is 5 commits behind head on develop.

❗ There is a different number of reports uploaded between BASE (ea7f56c) and HEAD (2b380b6). Click for more details.

HEAD has 4 uploads less than BASE

Flag	BASE (ea7f56c)	HEAD (2b380b6)
cannon-go-tests-32	3	1
cannon-go-tests-64	3	1

Additional details and impacted files

@@             Coverage Diff              @@
##           develop   #13062       +/-   ##
============================================
- Coverage    68.78%   44.24%   -24.55%     
============================================
  Files           56      798      +742     
  Lines         4665    71607    +66942     
============================================
+ Hits          3209    31684    +28475     
- Misses        1274    37347    +36073     
- Partials       182     2576     +2394     

Flag	Coverage Δ
cannon-go-tests-32	61.85% <ø> (-2.02%)	⬇️
cannon-go-tests-64	56.72% <ø> (-1.66%)	⬇️

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see 750 files with indirect coverage changes