Update subxt requirement from 0.29.0 to 0.30.0

Updates the requirements on [subxt](https://github.com/paritytech/subxt) to permit the latest version.
- [Release notes](https://github.com/paritytech/subxt/releases)
- [Changelog](https://github.com/paritytech/subxt/blob/master/CHANGELOG.md)
- [Commits](paritytech/subxt@v0.29.0...v0.30.0)

---
updated-dependencies:
- dependency-name: subxt
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]

Cargo.toml

@@ -64,7 +64,7 @@ serde_json = { version = "1.0.81" }
 sha2 = { version = "0.10" }
 sha3 = { version = "0.10" }
 static_assertions = { version = "1.1" }
-subxt = { version = "0.29.0" }
+subxt = { version = "0.30.0" }
 syn = { version = "2" }
 synstructure = { version = "0.13.0" }
 tokio = { version = "1.18.2" }