fix attrs==25.2.0 compatibility

[jakkdl]

fixes #13290

[jakkdl]

does this need a newsfragment?

[webknjaz]

Well, this seems user-facing. So I'd say yes.

[The-Compiler]

Not user-facing in the sense of "people using pytest". However, we have a contrib type for news entries, and it would probably fit there (from changelog/README.rst):

• contrib: stuff that affects the contributor experience. e.g. Running tests, building the docs, setting up the development environment.

[nicoddemus]

I agree with @webknjaz that this is user facing, because without this fix, pytest support for attrs==25.2.0 does not work properly.

I suggest 13291.bugfix.rst:

Fixed support for ``attrs 25.2``.

[Pierre-Sassoulas]

I also think it's user facing. Maybe 'fixed repr of attr object in assertion for attr 25.2' ?

[The-Compiler]

Oh, right. Somehow I assumed this was only in the self-test file. My bad!

[bluetech]

In order to unbreak CI I'll add a changelog based on @nicoddemus and @Pierre-Sassoulas suggestions and merge.

[patchback]

Backport to 8.3.x: 💚 backport PR created

✅ Backport PR branch: patchback/backports/8.3.x/4933d9223ffb3e9c1f11a4a2623be5d32672e071/pr-13291

Backported as #13294

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