chore: CI: bump dawidd6/action-download-artifact from 2 to 6 (#5964) · leanprover/lean4@0181418

Canceling since a higher priority waiting request for 'CI-refs/heads/master-push' exists

The operation was canceled.

Input 'save-always' has been deprecated with message: save-always does not work as intended and will be removed in a future release. A separate `actions/cache/restore` step should be used instead. See https://github.com/actions/cache/tree/main/save#always-save-cache for more details.