ci: update actions and restore Go caching

[davidpavlovschi]

Summary

• update the first-party workflow actions to their current Node 24-based major releases
• check out the repository before setup-go in the normal CI matrix so setup-go can hash go.sum and restore its cache
• keep the explicit GORM and badge module caches, while disabling the redundant setup-go cache in those jobs

Why

The master run after #156 passed all nine CI jobs but emitted a cache warning in every job because setup-go ran before checkout. GitHub also warned that checkout v4 and setup-go v5 target deprecated Node 20.

Validation

• all workflow YAML parses successfully
• git diff --check passes
• action versions match the current official releases: checkout v7, setup-go v7, cache v6, and upload-artifact v7

This changes CI plumbing only; project code and test commands remain unchanged.