Bump fixed-hash from 0.7.0 to 0.8.0

Bumps [fixed-hash](https://github.com/paritytech/parity-common) from 0.7.0 to 0.8.0.
- [Release notes](https://github.com/paritytech/parity-common/releases)
- [Commits](https://github.com/paritytech/parity-common/compare/fixed-hash-v0.7.0...fixed-hash-v0.8.0)

---
updated-dependencies:
- dependency-name: fixed-hash
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

bridges/primitives/chain-millau/Cargo.toml

@@ -13,7 +13,7 @@ license = "GPL-3.0-or-later WITH Classpath-exception-2.0"
 bp-beefy = { path = "../beefy", default-features = false }
 bp-messages = { path = "../messages", default-features = false }
 bp-runtime = { path = "../runtime", default-features = false }
-fixed-hash = { version = "0.7.0", default-features = false }
+fixed-hash = { version = "0.8.0", default-features = false }
 hash256-std-hasher = { version = "0.15.2", default-features = false }
 impl-codec = { version = "0.6", default-features = false }
 impl-serde = { version = "0.4.0", optional = true }