stop cargo publish complaining about * dep

would've been nice if cargo-publish --dry-run would have warned about this

Cargo.toml

@@ -30,7 +30,7 @@ bytes = { version = "1", optional = true }
 
 [dev-dependencies]
 magnus = { path = ".", features = ["embed", "rb-sys-interop"] }
-rb-sys = { version = "*", default-features = false, features = ["stable-api-compiled-fallback"] }
+rb-sys = { version = "0.9", default-features = false, features = ["stable-api-compiled-fallback"] }
 
 [build-dependencies]
 rb-sys-env = "0.1.2"