Wagtail 6.4 Support

[ianmeigh]

This PR adds Wagtail 6.4 Support with minor updates to the tox config.

[codecov-commenter]

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.13%. Comparing base (a0aa5b5) to head (251431c).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #860   +/-   ##
=======================================
  Coverage   93.13%   93.13%           
=======================================
  Files          47       47           
  Lines        4241     4241           
  Branches      550      550           
=======================================
  Hits         3950     3950           
  Misses        174      174           
  Partials      117      117           

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[nickmoreton]

Great thanks