Update prometheus-client requirement from 0.21 to 0.22 (AFLplusplus#2197

)

Updates the requirements on [prometheus-client](https://github.com/prometheus/client_rust) to permit the latest version.
- [Release notes](https://github.com/prometheus/client_rust/releases)
- [Changelog](https://github.com/prometheus/client_rust/blob/master/CHANGELOG.md)
- [Commits](prometheus/client_rust@v0.21.0...v0.22.2)

---
updated-dependencies:
- dependency-name: prometheus-client
  dependency-type: direct:production
...

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

libafl/Cargo.toml

@@ -170,7 +170,7 @@ libm = "0.2.2"
 ratatui = { version = "0.23.0", default-features = false, features = ['crossterm'], optional = true } # Commandline rendering, for TUI Monitor
 crossterm = { version = "0.27.0", optional = true }
 
-prometheus-client = { version = "0.21", optional = true } # For the prometheus monitor
+prometheus-client = { version = "0.22", optional = true } # For the prometheus monitor
 tide = { version = "0.16.0", optional = true }
 async-std = { version = "1.12.0", features = ["attributes"], optional = true }
 futures = { version = "0.3.24", optional = true }