Align the cache directory with the UNIX XDG Base Directory Specification

[pepicrft]

Short description 📝

The convention for the caching directory in many UNIX tools is captured in the XDG Base Directory Specification. The cache directory should be the one specified by the XDG_CACHE environment variable falling back to the ~/.cache directory. This PR aligns us with that convention.

How to test the changes locally 🧐

All the workflows use caching so if you try to use any of them it should succeed.

Contributor checklist ✅

• The code has been linted using run mise run lint:fix
• The change is tested via unit testing or acceptance testing, or both
• The title of the PR is formulated in a way that is usable as a changelog entry
• In case the PR introduces changes that affect users, the documentation has been updated

Reviewer checklist ✅

• The code architecture and patterns are consistent with the rest of the codebase
• Reviewer has checked that, if needed, the PR includes the label changelog:added, changelog:fixed, or changelog:changed, and the title is usable as a changelog entry