Test failure with Python 3.11

[fabaff]

The build process of aenum for nixpkgs fails on Python 3.11 while it works on Python 3.10.

running install tests
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ERROR: test_stdlib_inheritence (aenum.test_v3.TestEnumV3.test_stdlib_inheritence)
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Traceback (most recent call last):
  File "/nix/store/4aps5crh9miyrkxvxs8z3p51iy9i6mh0-python3.11-aenum-3.1.11/lib/python3.11/site-packages/aenum/test_v3.py", line 91, in test_stdlib_inheritence
    class AStrEnum(StrFlag):
                   ^^^^^^^
NameError: name 'StrFlag' is not defined

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FAIL: test_extend_flag_backwards_stdlib (aenum.test_v3.TestExtendEnumV3.test_extend_flag_backwards_stdlib)
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Traceback (most recent call last):
  File "/nix/store/4aps5crh9miyrkxvxs8z3p51iy9i6mh0-python3.11-aenum-3.1.11/lib/python3.11/site-packages/aenum/test_v3.py", line 1899, in test_extend_flag_backwards_stdlib
    self.assertTrue(Color(16) is Color.MAGENTA)
AssertionError: False is not true

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Ran 443 tests in 0.594s

FAILED (failures=1, errors=1)