Downgrade mockito to satisfy MSRV

Author: G8XSU

Cargo.toml

@@ -34,6 +34,6 @@ prost-build = { version = "0.11.3" }
 reqwest =  { version = "0.11.13", default-features = false, features = ["rustls-tls", "blocking"] }
 
 [dev-dependencies]
-mockito = "0.31.1"
+mockito = "0.28.0"
 proptest = "1.1.0"
 tokio = { version = "1.22.0", features = ["macros"]}