Migrate default repository branch to main

[ml-evs]

Somewhat overdue, will have a search around GitHub to see if this will break any of the automations outside this repo (e.g., the validator action).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.83%. Comparing base (14a63db) to head (e7ad744).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2136      +/-   ##
==========================================
- Coverage   90.85%   90.83%   -0.03%     
==========================================
  Files          75       75              
  Lines        4824     4824              
==========================================
- Hits         4383     4382       -1     
- Misses        441      442       +1     

Flag	Coverage Δ
project	90.83% <ø> (-0.03%)	⬇️
validator	90.83% <ø> (-0.03%)	⬇️

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