PEP750: test that `Template` and `Interpolation` types are final

[sobolevn]

Bug report

They should be final, because a lot of places use _PyInterpolation_CheckExact and _PyTemplate_CheckExact.

And they are final right now, we just need to test this. I have a PR ready.

@lysnikolaou sorry that I am finding this issues just now, but it is better late than never :)

Linked PRs

• gh-133211: Test that PEP750 types are final #133212

[lysnikolaou]

No need to say sorry. Thanks for looking into these! ❤