Relax check for SystemError

Summary: In 3.15 this error message is colored and includes the ANSI escape codes for the colorization so the in check doesn't match. Just look for `SystemError`

Reviewed By: yoney

Differential Revision: D85976047

fbshipit-source-id: 7c7643b7c4cf00ec0fca47991a0d677d591f6338

Author: DinoV

cinderx/PythonLib/test_cinderx/test_cpython_overrides/test_capi.py

@@ -27,7 +27,7 @@ def test_getitem_with_error(self) -> None:
         )
         rc, out, err = assert_python_failure("-c", code)
         err = decode_stderr(err)
-        if "SystemError: " not in err:
+        if "SystemError" not in err:
             self.assertRegex(
                 err,
                 r"Fatal Python error: _Py_CheckSlotResult: "