Fix further Wagtail `main` failures and tidy up GH Action/Makefile

[zerolab]

This PR:

• adds a callable for the page revision model (with Wagtail 4.0, that will be wagtailcore.Revision ref: https://github.com/wagtail/wagtail/pull/8441) -- should fix the nightly test failures
• updates the test GitHub Action to:
  • cancel previous in-progress jobs for the same branch/PR
  • cache tox
  • use newer action versions from GitHub
• adds a few more commands to the Makefile

[codecov-commenter]

Codecov Report

Merging #572 (2924c39) into main (7d6278c) will increase coverage by 0.11%. The diff coverage is 60.00%.

@@            Coverage Diff             @@
##             main     #572      +/-   ##
==========================================
+ Coverage   91.44%   91.55%   +0.11%     
==========================================
  Files          47       47              
  Lines        3894     3898       +4     
  Branches      591      592       +1     
==========================================
+ Hits         3561     3569       +8     
+ Misses        192      186       -6     
- Partials      141      143       +2     

Impacted Files	Coverage Δ
wagtail_localize/compat.py	51.85% <50.00%> (-0.33%)	:arrow_down:
wagtail_localize/models.py	95.57% <100.00%> (-0.15%)	:arrow_down:
wagtail_localize/components.py	82.69% <0.00%> (-1.93%)	:arrow_down:
wagtail_localize/views/convert.py	71.62% <0.00%> (+1.35%)	:arrow_up:
wagtail_localize/views/edit_translation.py	85.44% <0.00%> (+1.53%)	:arrow_up:

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