Temporarily ignore collection_is_never_read on FlattenSkipDeserializing

    error: collection is never read
       --> test_suite/tests/test_gen.rs:723:25
        |
    723 |     #[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:23:9
        |
    23  | #![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

@@ -720,11 +720,14 @@ fn test_gen() {
         flat: StdOption<T>,
     }
 
-    #[derive(Serialize, Deserialize)]
-    pub struct FlattenSkipDeserializing<T> {
-        #[serde(flatten, skip_deserializing)]
-        flat: T,
-    }
+    #[allow(clippy::collection_is_never_read)] // FIXME
+    const _: () = {
+        #[derive(Serialize, Deserialize)]
+        pub struct FlattenSkipDeserializing<T> {
+            #[serde(flatten, skip_deserializing)]
+            flat: T,
+        }
+    };
 
     #[derive(Serialize, Deserialize)]
     #[serde(untagged)]