Fixes #851 - Missing pagination on locale index view

[Marvinrose]

What

Fixes #851 - The Settings, Locales page was capped at 20 locales with no way to access the rest.

Why

IndexView used a custom template (wagtaillocales/index.html) that overrode Wagtail's generic {% block listing %} with its own table loop. This bypassed Wagtail's built-in pagination entirely, meaning sites with 21+ locales could not access or manage the hidden ones.

Fix

• Removed template_name from IndexView so it uses Wagtail's generic index template, which includes pagination automatically
• Updated the custom template to extend the generic template while preserving the Usage column (page counts per locale)
• Updated test_simple to assert the generic template is used instead of the custom one

Testing

All TestLocaleIndexView tests pass:

[Marvinrose]

I also noticed the 10 CI failures are caused by a pre-existing bug where Wagtail renamed produced_error_message to get_error_message in a newer version. The fix is to add produced_error_message = None to both CreateView and EditView so they're compatible with the latest Wagtail. I've opened issue #904 and submitted a fix in PR #905.

[zerolab]

#905 is now merged. Can you rebase, and also add a test please?

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.03%. Comparing base (8ba01e7) to head (774871b).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #903   +/-   ##
=======================================
  Coverage   93.02%   93.03%           
=======================================
  Files          47       47           
  Lines        4245     4251    +6     
  Branches      551      552    +1     
=======================================
+ Hits         3949     3955    +6     
  Misses        177      177           
  Partials      119      119           

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[Marvinrose]

Hi @zerolab

Rebased and added pagination test as requested.