Run tests on pushes to main

[johannaengland]

A classic copy and paste mistake from copying from Zino, which uses the "master" branch name instead...
I noticed this when trying to check if the codecov uploading is working here, but noticed that it has not yet, which made me suspicious...

[johannaengland]

But very practical - now this PR can actually be used to see if codecov uploading is working 😁

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 70.32%. Comparing base (ddfbd8c) to head (9fd87b9).
Report is 10 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #66      +/-   ##
==========================================
- Coverage   70.49%   70.32%   -0.18%     
==========================================
  Files          13       13              
  Lines        1427     1432       +5     
==========================================
+ Hits         1006     1007       +1     
- Misses        421      425       +4     

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[johannaengland]

But very practical - now this PR can actually be used to see if codecov uploading is working 😁

And we see that it is working! (Even though CodeCov complains that it is missing reports on the main branch, which is what this PR will fix)