test: fix `common.mustNotCall()` usage in HTTP test

The argument to `common.mustNotCall()` is a message, not a function.

PR-URL: https://github.com/nodejs/node/pull/24750


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Anto Aravinth <anto.aravinth.cse@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>