Revert "fix(deps): update github.com/thanos-io/objstore digest to c3ccc5d (main)"

[dimitarvdimitrov]

Reverts #7466

There still seems to be an issue, as reported by @jhalterman

msg="failed to read cluster seed file from object storage" err="Get \"https://storage.googleapis.com/dev-us-central-0-mimir-dev-11-blocks/__mimir_cluster%2Fmimir_cluster_seed.json\": oauth2: cannot fetch token: 400 Bad Request\nResponse: {\"error\":\"invalid_scope\",\"error_description\":\"Invalid OAuth scope or ID token audience provided.\"}"