pythongh-117606: Truncate extremely long error message in test_exceptions (python#117670)

Co-authored-by: Alex Waygood <Alex.Waygood@Gmail.com>

Author: nineteendo

Lib/test/test_exceptions.py

@@ -1451,7 +1451,8 @@ def test_recursion_normalizing_infinite_exception(self):
         """
         rc, out, err = script_helper.assert_python_failure("-c", code)
         self.assertEqual(rc, 1)
-        self.assertIn(b'RecursionError: maximum recursion depth exceeded', err)
+        expected = b'RecursionError: maximum recursion depth exceeded'
+        self.assertTrue(expected in err, msg=f"{expected!r} not found in {err[:3_000]!r}... (truncated)")
         self.assertIn(b'Done.', out)