Fix deprecation warning about test function returning non-None

Summary:
All `test_` functions should return None, this one doesn't and raises a noisy
DeprecationWarning.

Reviewed By: DinoV

Differential Revision: D81061284

fbshipit-source-id: a8d2ac156f13d32b55e8ed7bdf5a56fc1a8a6e6e

Author: alexmalyshev

cinderx/PythonLib/test_cinderx/test_cinderjit.py

@@ -798,9 +798,12 @@ def test_tmp_name2(self) -> None:
 
 class JITCompileCrasherRegressionTests(StaticTestBase):
     @cinder_support.failUnlessJITCompiled
-    def test_isinstance_optimization(self) -> None:
+    def isinstance_optimization(self) -> bool:
         return isinstance(None, int) and True
 
+    def test_isinstance_optimization(self) -> None:
+        self.assertFalse(self.isinstance_optimization())
+
     @cinder_support.failUnlessJITCompiled
     def _fstring(self, flag, it1, it2):
         for a in it1: