1 test fails: AttributeError: can't set attribute

[yurivict]

======================================================================
ERROR: test_cache_write_unpicklable_object (tests.test_djangocache.DiskCacheTests)
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Traceback (most recent call last):
  File "/disk-samsung/freebsd-ports/devel/py-diskcache/work-py39/python-diskcache-5.4.0/tests/test_djangocache.py", line 873, in test_cache_write_unpicklable_object
    fetch_middleware.cache = cache
AttributeError: can't set attribute

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Ran 64 tests in 19.004s

Version: 5.4.0
Python-3.9
FreeBSD 13.1

[grantjenks]

Dupe of #260