gh-145492: fix regression test for defaultdict factory repr

[KowalskiThomas]

What is this PR?

This PR fixes the regression test introduced in #145761 and that did not properly reproduce the issue.

Running the test without the repr changes now properly crashes.

% ./python.exe -m unittest test.test_defaultdict
..........E..
======================================================================
ERROR: test_repr_recursive_factory (test.test_defaultdict.TestDefaultDict.test_repr_recursive_factory)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/Users/thomas.kowalski/Documents/cpython/Lib/test/test_defaultdict.py", line 219, in test_repr_recursive_factory
    r = repr(dd)
  File "/Users/thomas.kowalski/Documents/cpython/Lib/test/test_defaultdict.py", line 215, in __repr__
    return f"ProblematicFactory for {dd}"
                                    ^^^^
  File "/Users/thomas.kowalski/Documents/cpython/Lib/test/test_defaultdict.py", line 215, in __repr__
    return f"ProblematicFactory for {dd}"
                                    ^^^^
  File "/Users/thomas.kowalski/Documents/cpython/Lib/test/test_defaultdict.py", line 215, in __repr__
    return f"ProblematicFactory for {dd}"
                                    ^^^^
  [Previous line repeated 981 more times]
RecursionError: maximum recursion depth exceeded

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Ran 13 tests in 1.742s