fuzz: run the GC pass when fuzzing

When we round-trip a module through walrus, also run our GC pass on it. This
will help us catch bugs where the GC pass removes something that is actually in
use.

crates/fuzz-utils/src/lib.rs

@@ -105,8 +105,9 @@ where
     }
 
     fn round_trip_through_walrus(&self, wasm: &[u8]) -> Result<Vec<u8>> {
-        let module =
+        let mut module =
             walrus::Module::from_buffer(&wasm).context("walrus failed to parse the wasm buffer")?;
+        walrus::passes::gc::run(&mut module);
         let buf = module.emit_wasm();
         Ok(buf)
     }