That’s incorrect - bugs are fixed on stable as well: https://github.com/discourse/discourse/commits/stable
And because there are (almost) no new features, there are virtually no new bugs being introduced.
But the question wasn’t if, it was how:
Wait until 2.4.0 is out and then find the line #version: tests-passed in your app.yml , change it to version: stable , and rebuild.
(don’t forget to remove the # as well)