Remove unused dependencies from juniper_codegen_tests crate

Author: tyranron

tests/codegen/Cargo.toml

@@ -10,8 +10,6 @@ rustversion = "1.0"
 [dev-dependencies]
 futures = "0.3"
 juniper = { path = "../../juniper" }
-serde_json = "1.0"
-tokio = { version = "1.0", features = ["rt", "time", "macros"] }
 trybuild = "1.0.63"
 
 [lints.clippy]

tests/codegen/src/lib.rs

@@ -3,6 +3,12 @@
 // TODO: [Object] Type Validation: §4 (interfaces) for objects
 // TODO: [Non-Null] §1 A Non‐Null type must not wrap another Non‐Null type.
 
+#[cfg(test)]
+mod for_codegen_tests_only {
+    use futures as _;
+    use juniper as _;
+}
+
 #[rustversion::stable]
 #[test]
 fn test_failing_compilation() {