Fix a warning about unnecessary mut in AutoAssertNoGc

Author: fitzgen

crates/wasmtime/src/store.rs

@@ -305,6 +305,7 @@ where
     T: std::ops::DerefMut<Target = StoreOpaque>,
 {
     pub fn new(mut store: T) -> Self {
+        drop(&mut store);
         #[cfg(debug_assertions)]
         {
             let prev_okay = store.externref_activations_table.set_gc_okay(false);