Align main with 1.12.x

[zerolab]

• drops Wagtail < 6.3
• removes shims / conditionals for earlier versions
• updates the translations

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.02%. Comparing base (7cae469) to head (72e726d).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #865      +/-   ##
==========================================
- Coverage   93.26%   93.02%   -0.25%     
==========================================
  Files          47       47              
  Lines        4249     4242       -7     
  Branches      552      551       -1     
==========================================
- Hits         3963     3946      -17     
- Misses        171      177       +6     
- Partials      115      119       +4     

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