doc: fix buffer api example code's token error

Buffer's Blob api example code has some token error

PR-URL: https://github.com/nodejs/node/pull/40125


Reviewed-By: Qingyu Deng <i@ayase-lab.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: James M Snell <jasnell@gmail.com>