Resolve deprecation warnings of bs4 library

[emmanuel-ferdman]

Summary

This small PR resolves the bs4 library deprecation warnings:

/home/runner/work/wagtail-localize/wagtail-localize/wagtail_localize/strings.py:478: DeprecationWarning: Call to deprecated method replaceWith. (Replaced by replace_with) -- Deprecated since version 4.0.0.

/home/runner/work/wagtail-localize/wagtail-localize/wagtail_localize/strings.py:363: DeprecationWarning: Call to deprecated method replaceWith. (Replaced by replace_with) -- Deprecated since version 4.0.0.

/home/runner/work/wagtail-localize/wagtail-localize/wagtail_localize/strings.py:476: DeprecationWarning: Call to deprecated method findAll. (Replaced by find_all) -- Deprecated since version 4.0.0.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 93.02%. Comparing base (9646cec) to head (97699e3).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #867   +/-   ##
=======================================
  Coverage   93.02%   93.02%           
=======================================
  Files          47       47           
  Lines        4242     4242           
  Branches      551      551           
=======================================
  Hits         3946     3946           
  Misses        177      177           
  Partials      119      119           

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[zerolab]

Thank you for this!