Fix warning about unused_must_use for Box::from_raw (#860)

Author: ehuss

src/odb.rs

@@ -514,7 +514,7 @@ impl<'repo> Drop for OdbPackwriter<'repo> {
                 None => (),
             };
 
-            Box::from_raw(self.progress_payload_ptr);
+            drop(Box::from_raw(self.progress_payload_ptr));
         }
     }
 }