availableLanguages ISO country/language codes should be lowercase, but intendedAudience.countries MUST BE uppercase

[rklec]

I came from #275 and thanks to my IDE noticed a "discrepancy" in the standard.

As for the key intendedAudience.countries it forces uppercase letters/ISO language codes (in the latest standard apparently; cannot find that change in the release docs though), as https://editor.opencode.de/ still gave me lowercase letters):

This seems to be compliant as per https://yml.publiccode.tools/schema.core.html#key-intendedaudience-countries:

All countries are specified using lowercase (deprecated) or uppercase ISO 3166-1 alpha-2 two-letter country codes.

(which BTW, the example in https://guide.opencode.de/assets/code/publiccode.yml still does explicitly wrong)

However, the key localisation.availableLanguages apparently uses lowercase letters?

Example: "it", "en", "sl-IT-nedis"

https://yml.publiccode.tools/schema.core.html#key-localisation-availablelanguages

I know countries and languages are something different and the last one follow a different standard, but anyway, this was very confusing for me.