bump Lightning 2.1+

[joao-alex-cunha]

What does this PR do?

Makes lightning-Graphcore compatible with latest Lightning versions. Tested 2.1.1 and also master.
Note that I'm also using the latest Graphcore SDK (version 3.4)

There are a number of tests previously marked as failing that now pass.

A small caveat: in test test_warning_if_ipus_not_used the error message thrown by the Trainer has changed and I couldn't make the regex match. I believe it is to do with the quote marks. So I simplified the check to just verify if there is a UserWarning without verifying the error message itself.

closes #51

[Borda]

@joao-alex-cunha could you pls allow maintainers to edit the PR?
would need to resolve merge conflicts and complain with pre-commit...

[Borda]

@joao-alex-cunha how id it going here? :)

[joao-alex-cunha]

@Borda apologies for the delay. Between missing the first message and being busy working on other stuff, I could only get this done today. Thank you for your patience.

[Borda]

@joao-alex-cunha could you pls run precommit on this PR, seems I can't push fix to your branch due to some protections coming with your fork repo... 🦩

[joao-alex-cunha]

Hi @Borda, I ran pre-commit and merged main onto this PR. Let me know if you need anything else.

[Borda]

I ran pre-commit and merged main onto this PR. Let me know if you need anything else.

It seems that the provided agents are offline, so we need to wait until they get back live and run tests...