Summary:
we expect a sha256 value, not a sha1. <release_url>.sha has only ever been a sha256 value,
so we cannot use it.

Test Plan: created a release and then a universe with the release

Reviewers: muthu, anijhawan

Reviewed By: muthu

Subscribers: svc_phabricator, yugaware

Differential Revision: https://phorge.dev.yugabyte.com/D39263