pythongh-105699: Re-enable the Multiple-Interpreters Stress Tests (pythongh-107572)

We had disabled them due to crashes they exposed, which have since been fixed.

Author: ericsnowcurrently

Lib/test/test_interpreters.py

@@ -464,7 +464,6 @@ def test_bytes_for_script(self):
     # test_xxsubinterpreters covers the remaining Interpreter.run() behavior.
 
 
-@unittest.skip('these are crashing, likely just due just to _xxsubinterpreters (see gh-105699)')
 class StressTests(TestBase):
 
     # In these tests we generally want a lot of interpreters,