pin trio to <0.25.0 due to breaking changes

[axiomiety]

0.25.0 causes some tests to fail - c.f. release notes

[trio-bot[bot]]

Hey @axiomiety, it looks like that was the first time we merged one of your PRs! Thanks so much! :tada: :birthday:

If you want to keep contributing, we'd love to have you. So, I just sent you an invitation to join the python-trio organization on Github! If you accept, then here's what will happen:

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If you want to read more, here's the relevant section in our contributing guide.

Alternatively, you're free to decline or ignore the invitation. You'll still be able to contribute as much or as little as you like, and I won't hassle you about joining again. But if you ever change your mind, just let us know and we'll send another invitation. We'd love to have you, but more importantly we want you to do whatever's best for you.

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