tools: specify rule disabled in test-assert.js

Instead of disabling all ESLint rules on two lines in test-assert.js,
specify the rule that needs to be disabled.

PR-URL: https://github.com/nodejs/node/pull/22563


Reviewed-By: Vse Mozhet Byt <vsemozhetbyt@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Trivikram Kamat <trivikr.dev@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>