lxml pinning / Python 3.12 support for MacOS

[efecan-circlelabs]

Hello,

I'm unable to find a reason why lxml is pinned here
https://github.com/adbar/htmldate/blob/master/setup.py#L121-L122

It's breaking my local dev which is running on MacOS and encountering the pinned version which doesn't compile for Python 3.12 (later versions of lxml compile just fine).

For the mean time I've fork'd this repo and removed the pinning.

Please advice, happy to make any required PRs!
Thanks.