Bump unsigned-varint from 0.6.0 to 0.7.0

Bumps [unsigned-varint](https://github.com/paritytech/unsigned-varint) from 0.6.0 to 0.7.0.
- [Release notes](https://github.com/paritytech/unsigned-varint/releases)
- [Changelog](https://github.com/paritytech/unsigned-varint/blob/master/CHANGELOG.md)
- [Commits](paritytech/unsigned-varint@v0.6.0...v0.7.0)

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

Author: dependabot[bot]

Cargo.lock

@@ -57,7 +57,7 @@ sp-core = { version = "3.0.0", path = "../../primitives/core" }
 sp-runtime = { version = "3.0.0", path = "../../primitives/runtime" }
 sp-utils = { version = "3.0.0", path = "../../primitives/utils" }
 thiserror = "1"
-unsigned-varint = { version = "0.6.0", features = ["futures", "asynchronous_codec"] }
+unsigned-varint = { version = "0.7.0", features = ["futures", "asynchronous_codec"] }
 void = "1.0.2"
 wasm-timer = "0.2"
 zeroize = "1.2.0"