Executor: Incorrect description of AggregationExecutor::Next()

In file `src/include/execution/executors/aggregation_executor.h`:

```cpp
/**
 * Yield the next tuple from the insert.
 * @param[out] tuple The next tuple produced by the insert
 * @param[out] rid The next tuple RID produced by the insert
 * @return `true` if a tuple was produced, `false` if there are no more tuples
 */
auto Next(Tuple *tuple, RID *rid) -> bool override;
```