fuzz: fix unused Result clippy finding.

```
warning: unused `std::result::Result` that must be used
  --> fuzzers/persist.rs:14:5
   |
14 |     T::read(&mut rdr);
   |     ^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_must_use)]` on by default
   = note: this `Result` may be an `Err` variant, which should be handled
```

fuzz/fuzzers/persist.rs

@@ -11,7 +11,8 @@ where
     T: Codec,
 {
     let mut rdr = Reader::init(data);
-    T::read(&mut rdr);
+
+    let _ = T::read(&mut rdr);
 }
 
 fuzz_target!(|data: &[u8]| {