build(deps): update unsigned-varint requirement from 0.7 to 0.8

Updates the requirements on [unsigned-varint](https://github.com/paritytech/unsigned-varint) to permit the latest version.
- [Changelog](https://github.com/paritytech/unsigned-varint/blob/master/CHANGELOG.md)
- [Commits](paritytech/unsigned-varint@v0.7.0...v0.8.0)

---
updated-dependencies:
- dependency-name: unsigned-varint
  dependency-type: direct:production
...

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

Cargo.toml

@@ -22,7 +22,7 @@ multihash = "0.19"
 percent-encoding = "2.1.0"
 serde = "1.0.70"
 static_assertions = "1.1"
-unsigned-varint = "0.7"
+unsigned-varint = "0.8"
 url = { version = "2.1.0", optional = true, default-features = false }
 libp2p-identity = { version = "0.2.0", features = ["peerid"] }