Rename return parameter (#3413)

contracts/governance/TimelockController.sol

@@ -131,7 +131,7 @@ contract TimelockController is AccessControl, IERC721Receiver, IERC1155Receiver
      * @dev Returns whether an id correspond to a registered operation. This
      * includes both Pending, Ready and Done operations.
      */
-    function isOperation(bytes32 id) public view virtual returns (bool pending) {
+    function isOperation(bytes32 id) public view virtual returns (bool registered) {
         return getTimestamp(id) > 0;
     }