feat: create a github action that tags a pr that modifies a po file as "translations

[lwasser]

In the translating.md file
https://github.com/pyOpenSci/python-package-guide/blob/main/TRANSLATING.md there is a TODO that suggests it would be useful to tag new pr's that are translation related.

This could be a CI Action that looks to see if the pr is hitting a .po file and if it is, the translation tag is applied. There might be a better way to do this too; I'm just thinking out loud that looking to see if the pr hits files in that dir might be a good way to implement an autotag!!

[wahajmasood]

Interested in this — planning to implement a '.github/workflows/label-translations.yml' that fires on 'pull_request' events touching 'locales/**/*.po'. It'd apply both the generic 'translations' label and the matching per-language 'lang-XX' label (extracted from the changed file's 'locales//' path and uppercased to match the existing 'lang-ES' / 'lang-JA' / 'lang-PT' labels). Handles multi-language PRs by applying each 'lang-XX' it detects. Will open a PR in the next day or two.