Enable collection_is_never_read nursury lint in test

    error: collection is never read
       --> test_suite/tests/test_gen.rs:722:25
        |
    722 |     #[derive(Serialize, Deserialize)]
        |                         ^^^^^^^^^^^
        |
        = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#collection_is_never_read
    note: the lint level is defined here
       --> test_suite/tests/test_gen.rs:22:9
        |
    22  | #![deny(clippy::collection_is_never_read)]
        |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        = note: this error originates in the derive macro `Deserialize` (in Nightly builds, run with -Z macro-backtrace for more info)

test_suite/tests/test_gen.rs

@@ -19,6 +19,7 @@
     clippy::trivially_copy_pass_by_ref,
     clippy::type_repetition_in_bounds
 )]
+#![deny(clippy::collection_is_never_read)]
 
 use serde::de::{Deserialize, DeserializeOwned, Deserializer};
 use serde::ser::{Serialize, Serializer};