fix(prometheus): disable libtest bench harness to fix benchmark CI (#3519)

Author: souyang-dev

opentelemetry-prometheus/Cargo.toml

@@ -15,6 +15,9 @@ license = "Apache-2.0"
 edition = "2021"
 rust-version = "1.81.0"
 
+[lib]
+bench = false
+
 [package.metadata.docs.rs]
 all-features = true
 rustdoc-args = ["--cfg", "docsrs"]