Add a GH action to update the translation issues when .po files change

[flpm]

This is part 4 of the work to create scripts to help maintain translations and their GH issues.

1) Create a translation maintenance issue to track of translation maintenance work and subscribe to Slack #translations #780
2) Create a GH action to monitor when the English source of the guide and post a comment on the translation maintenance issue #781
3) Split the computation of translation stats from the Sphinx extension so scripts can use it #786
4) Create a GH action to keep the translation issues used by contributors up to date when po files change
5) Create a script to create new issues when a new language (or a new .po file) is created
6) Create a simple create-new-language.py script that maintainers can call to take all actions required to add a new language to the guide: creates the po files, adds the language to the list of languages, create the GH issues, etc.
7) Document everything in TRANSLATING.md, in a section for maintainers, explaining how this all works and how to use it.

What was done

• Added a new a GH action to check if the translation issues need to be updated and update them. Triggers every time .po files change on main. Checks all locales.
• Added a Python script refresh_translation_issues.py, called by the action
• Added tests for the python logic in test_refresh_translation_issues.py
• Added a template for the parent issue parent_issue_template.md - See an example of parent issue: Help translate the Python Packaging Guide into Greek #715
• Added a template for the sub-issue child_issue_template.md - See an example of sub-issue: Translate index.po into Greek #752
• Modified noxfile.py so the test-translation-scripts action works with the new tests

How to test

Run nox -s test-translation-scripts

AI disclosure

Claude code help me to write this code, I reviewed everything the AI wrote and take full responsibility for how it works.