build: touch tools/doc/node_modules after run

Currently, tools/doc/node_modules is not touched after running npm
install resulting in npm install being run every time. I missed this
while testing commit 88bff826 ("build:
make tools/doc/node_modules non-phony").

PR-URL: https://github.com/nodejs/node/pull/22350


Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>