chore(deps): update monero requirement from 0.19 to 0.21

Updates the requirements on [monero](https://github.com/monero-rs/monero-rs) to permit the latest version.
- [Release notes](https://github.com/monero-rs/monero-rs/releases)
- [Changelog](https://github.com/monero-rs/monero-rs/blob/main/CHANGELOG.md)
- [Commits](monero-rs/monero-rs@v0.19.0...v0.21.0)

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

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

Cargo.toml

@@ -18,7 +18,7 @@ fixed-hash = "0.8"
 hex = "0.4"
 http = "0.2"
 jsonrpc-core = "18"
-monero = { version = "0.19", features = ["serde"] }
+monero = { version = "0.21", features = ["serde"] }
 reqwest = { version = "0.11", default-features = false, features = ["json", "socks"] }
 serde = { version = "1", features = ["derive"] }
 serde_json = "1"