* Update `digest` and `blake2` requirement from 0.7 to 0.8

Updates the requirements on [digest](https://github.com/RustCrypto/traits) to permit the latest version.
- [Release notes](https://github.com/RustCrypto/traits/releases)
- [Commits](https://github.com/RustCrypto/traits/compare/digest_v0.7.2...digest-v0.8.1)

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>
Co-authored-by: Pratyush Mishra <pratyushmishra@berkeley.edu>