Use more aggresive caching for GitHub

[ErdaradunGaztea]

When listing repos, we can avoid performing pagination by sorting by created or updated instead of full_name. Or perhaps use conditional requests (https://docs.github.com/en/rest/overview/resources-in-the-rest-api#conditional-requests) to check if the cache expired. Or, preferably, combine both.
If sorting by updated, we can also optimize checking for DESCRIPTION files; re-check only those that were updated since then.