tools: add NODE_TEST_NO_INTERNET to the doc builder

At the moment the doc builder tries to access the internet
for CHANGELOG information and only falls back to local sources
after the connection fails or a 5 second timeout. This means
that the doc building could take at least 7 minutes on a
machine with hijacked connection to Github for useless network
attempts. This patch adds a NODE_TEST_NO_INTERNET environment
variable to directly bypass these attempts so that docs can be
built in reasonable time on a machine like that.

PR-URL: https://github.com/nodejs/node/pull/31849
Fixes: https://github.com/nodejs/node/issues/29918


Reviewed-By: Matheus Marchini <mat@mmarchini.me>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>