test: address flaky wpt/test-timers

Moving test harness from Parallel to Simple resolves most of the
failures. negative-settimeout.any.js still needs to be marked flaky.

Refs: https://github.com/nodejs/node/issues/37672

PR-URL: https://github.com/nodejs/node/pull/37691
Fixes: https://github.com/nodejs/node/issues/37672


Reviewed-By: Antoine du Hamel <duhamelantoine1995@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>