deps: bump prometheus-client from 0.19.0 to 0.20.0

Pull-Request: #3754.

Author: dependabot[bot]

Cargo.lock

@@ -12,4 +12,4 @@ hyper = { version = "0.14", features = ["server", "tcp", "http1"] }
 libp2p = { path = "../../libp2p", features = ["async-std", "metrics", "ping", "noise", "identify", "tcp", "yamux", "macros"] }
 log = "0.4.0"
 tokio = { version = "1", features = ["rt-multi-thread"] }
-prometheus-client = "0.19.0"
+prometheus-client = "0.20.0"

examples/metrics/Cargo.toml

@@ -27,7 +27,7 @@ libp2p-ping = { workspace = true, optional = true }
 libp2p-relay =  { workspace = true, optional = true }
 libp2p-swarm = { workspace = true }
 libp2p-identity = { workspace = true }
-prometheus-client = "0.19.0"
+prometheus-client = "0.20.0"
 
 [target.'cfg(not(target_os = "unknown"))'.dependencies]
 libp2p-gossipsub =  { workspace = true, optional = true }

misc/metrics/Cargo.toml

@@ -35,7 +35,7 @@ wasm-timer = "0.2.5"
 instant = "0.1.11"
 void = "1.0.2"
 # Metrics dependencies
-prometheus-client = "0.19.0"
+prometheus-client = "0.20.0"
 
 [dev-dependencies]
 async-std = { version = "1.6.3", features = ["unstable"] }