Importing ABC directly from collections module was removed in Python 3.9

[tirkarthi]

https://bugzilla.redhat.com/show_bug.cgi?id=1792921

demjson/test/test_demjson.py

Line 118 in 5bc6597

dict_mixin = collections.MutableMapping

Thanks for the library!

[ttii]

Hi, Gays, I make A modify for use demjson in Python 3.10 +
https://github.com/ttii/demjson
my be it is helpfor