build: add python 3.12 support

[theoparis]

WIP

[CLAassistant]

All committers have signed the CLA.

[theoparis]

Upon testing new changes I ran out of swap space running pip install -v . (8gb ram + zram) and it crashed my entire window manager.

[jessebot]

@theoparis is that necessary with the extra GHA jobs that were added? It looks like the 3.12 tests are failing (at least partially) because of trainer, which @eginhard submitted a PR for here: coqui-ai/Trainer#143 (which I just realized you also reacted to 😅 ) but it needs to be merged and released by @erogol.

In the meantime, for the sake of the test, can you point your trainer version at @eginhard's test branch here?
https://github.com/eginhard/coqui-trainer/tree/py312

Then, if you're still out of ram, I or perhaps other passersby, can help test this locally to verify it's all good to go, if you need, but the GitHub jobs would probably finish testing for 3.12 (or at least fail on something else).