Nondeterministic italic font rendering in tests

[aedm]

Sometimes we get subpixel differences in Kittest-based tests, mostly visible in italic fonts. It even happens on the same machine (macos).

Example snapshot & diff:

From this job:
https://github.com/rerun-io/rerun/actions/runs/18278486729/job/52035906199

[emilk]

I don't understand why it is non-deterministic, but I suspect the problem is aggravated by differences in the texture filtering of different platforms (which comes to play for italics, since they are just slanted textures of straight letters in egui).

• Difference in rendering on windows, linux and macOS emilk/egui#5295

[emilk]

Based on #11541 it seems like we mostly solved this with emilk/egui#7602