download_hash.py

Containerd use the same repository for releases of it's gRPC API (which
we are not interested in).
Conveniently, those releases have tags which are not valid version
number (being prefixed with 'api/').

This could also be potentially useful for similar cases.
The risk of missing releases because of this are low, since it would
require that a project issue a new release with an invalid format, then
switch back to the previous format (or we miss the fact it's not
updating for a long period of time).