class deprecated metaclass conflict

Hello,

Has describe in the test if you have different metaclass this will break all this current code. There was a situation before that was here to handle compatibility with python2 which by side effect solve this issue, see https://forge.extranet.logilab.fr/open-source/logilab-common/blob/1.5.2/logilab/common/deprecation.py#L126

While doing this I realized that the previous solution was actually way simpler and didn't present this bug and I don't understand why it has been chosen to move to a metaclass strategy so I simply went back to this previous approach.

This situation breaks CubicWeb sadly, I'm going to see if we can launch tests from other project in this CI to see if we breaks them.

Kind regards,

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