fix lightbeam warning;

crates/lightbeam/src/backend.rs

@@ -5533,7 +5533,7 @@ impl<'this, M: ModuleContext> Context<'this, M> {
             slice = rest;
         }
 
-        mem::replace(&mut self.block_state.stack, stack);
+        let _ = mem::replace(&mut self.block_state.stack, stack);
         Ok(())
     }
 

crates/lightbeam/src/function_body.rs

@@ -876,7 +876,7 @@ where
 
     ctx.epilogue();
 
-    mem::replace(&mut session.op_offset_map, op_offset_map);
+    let _ = mem::replace(&mut session.op_offset_map, op_offset_map);
 
     Ok(())
 }