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 88bff82 ("build:
make tools/doc/node_modules non-phony").

PR-URL: #22350
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Joyee Cheung <joyeec9h3@gmail.com>

Makefile

@@ -1074,6 +1074,7 @@ lint-md-build: tools/remark-cli/node_modules \
 tools/doc/node_modules: tools/doc/package.json
 ifeq ($(node_use_openssl),true)
 	cd tools/doc && $(call available-node,$(run-npm-install))
+	@touch $@
 else
 	@echo "Skipping tools/doc/node_modules (no crypto)"
 endif