gh-136442: Fix unittest to return exit code 5 when setUpClass raises an exception

[ueshin]

Fixes unittest to return exit code 5 when setUpClass raises an exception.

import unittest

class BugTest(unittest.TestCase):
    @classmethod
    def setUpClass(cls):
        raise ValueError("Simulated setup failure")

    def test_example(self):
        self.assertTrue(True)

• before

$ ./python.exe -m unittest bug_test.py
E
======================================================================
ERROR: setUpClass (bug_test.BugTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/.../cpython/bug_test.py", line 6, in setUpClass
    raise ValueError("Simulated setup failure")
ValueError: Simulated setup failure

----------------------------------------------------------------------
Ran 0 tests in 0.000s

FAILED (errors=1)
$ echo $?
5

• after

$ ./python.exe -m unittest bug_test.py
E
======================================================================
ERROR: setUpClass (bug_test.BugTest)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/.../cpython/bug_test.py", line 6, in setUpClass
    raise ValueError("Simulated setup failure")
ValueError: Simulated setup failure

----------------------------------------------------------------------
Ran 0 tests in 0.000s

FAILED (errors=1)
$ echo $?
1

• Issue: unittest may incorrectly return exit code 5 when setUpClass raises an exception #136442

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