Improve the CI and the translation in readthedocs

[rffontenelle]

This greatly improves the CI workflow of sphinx-doc-translations, by simplify some statements in CI workflow, removing obsolete PO files and removing obsolete Transifex resources.

• Notable changes to main.yml:

  • simplifies the original workflow, removing unnecessary statements like git fetch depth, git checkout master, git push actions (in favor of a simple "git push"), etc.¹
  • script updates.sh was split in generate_templates.sh (POT and .tx/config generation) and updates.sh (tx push and tx pull). This was required for the cleanup of POT and Transifex resources.²
  • script locale/lock-translations.py added to find obsolete resources in Transifex, lock for 3 days (time to a manual check) and then remove the resource if it still locked.³
  • Obsolete POT are being removed after lock-translations.py run and before updating translations ⁴
  • renames job name 'ubuntu' to update
  • Use python version '3' instead of '3.9' to follow Sphinx CI workflow settings
  • only commit when there is a change, avoiding error exit when there is nothing to commit
  • do not push commits when in a pull request to allow testing; commit is made, but isn't really pushed
  • limit write permissions to 'contents', instead of everything as 'write'

• New workflow file test-translations.yml ⁵:

  • triggered when *.po is changed on push or pull_request events
  • it builds translated docs and lint PO for all languages and show their errors
  • uses problem-matchers to annotate issues issues (i.e. show in summary and in committed files themselves)
  • this workflow hasn't run in this PR check, because it doesn't exist in master branch yet. See this action run in my fork for an example of run and the syntax errors in the translations.

Footnotes:

¹ Example of issue: In pull requests, changes to updates.sh in the branch would not be used because git checkout master was changing the current branch during the workflow run, effectively making the workflow use updates.sh from master branch.

² locking resources needed POT and .tx/config generated, but not the translations pulled. So splitting seemed to be the best alternative. Other alternative was to set up another GHA job in same file and duplicate lines of statements checkout, dependencies installation, etc.

³ Fixes #40

⁴ Fixes #42

⁵ Fixes #41

[rffontenelle]

https://readthedocs.org/api/v2/build/24311043.txt

loading translations [pt-br]... WARNING: reading error: /home/docs/checkouts/readthedocs.org/user_builds/sphinx-pt-br/checkouts/38/locale/pt-br/LC_MESSAGES/sphinx.po, expected only letters, got 'pt-br'

[rffontenelle]

@AA-Turner Would you like to review this? Asking just to know if I wait or merge