Bump proptest from 1.5.0 to 1.6.0 (#667)

Bumps [proptest](https://github.com/proptest-rs/proptest) from 1.5.0 to 1.6.0.
- [Release notes](https://github.com/proptest-rs/proptest/releases)
- [Changelog](https://github.com/proptest-rs/proptest/blob/main/CHANGELOG.md)
- [Commits](https://github.com/proptest-rs/proptest/commits)

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

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Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Cargo.lock

@@ -26,7 +26,7 @@ criterion = "0.4.0"
 serde_derive = { version = "1.0" }
 parity-scale-codec-derive = { path = "derive", default-features = false }
 quickcheck = "1.0"
-proptest = "1.5.0"
+proptest = "1.6.0"
 trybuild = "1.0.101"
 paste = "1"
 rustversion = "1"