Revert "src: skip test_fatal/test_threads for Debug builds"

This reverts commit 1fc4d43a.

PR-URL: https://github.com/nodejs/node/pull/39954


Reviewed-By: Michaël Zasso <targos@protonmail.com>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Darshan Sen <raisinten@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>