Fix cache usage in the CI and purge already existing and not used cache

[remyleone]

At the moment we have messages such as:

Restore cache failed: Dependencies file is not found in /home/runner/work/terraform-provider-scaleway/terraform-provider-scaleway. Supported file pattern: go.sum

It would be helpful to check all cache usage in the CI to ensure that it is used correctly. In particular we seem to have a LOT of caches: https://github.com/scaleway/terraform-provider-scaleway/actions/caches
It would be helpful to check the key for those cache to ensure that we can reuse as much as possible cache across the whole CI

[remyleone]

Fixed with #2678