fix pessimizing move in batch_executor

src/mongo/db/commands/write_commands/batch_executor.cpp:344:19: error: moving a temporary object prevents copy elision [-Werror,-Wpessimizing-move]

        wcError = std::move(toWriteConcernError(status, res));

                  ^

src/mongo/db/commands/write_commands/batch_executor.cpp:344:19: note: remove std::move call here

        wcError = std::move(toWriteConcernError(status, res));

                  ^~~~~~~~~~                                ~