tools: add linting rule for async IIFEs

The result of an async IIFE should always be handled in our tests,
typically by adding `.then(common.mustCall())` to verify that the
async function actually finishes executing at some point.

PR-URL: https://github.com/nodejs/node/pull/34363


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>