Fix egui on testbed

[ThierryBerger]

• Follow up to Update to Bevy 0.17 and rapier 0.29 along with dependencies nalgebra, glam dimforge/bevy_rapier#678 ; thanks for the PR!

After testing your PR locally, I realized testbeds were broken so I fixed it.

I can't push on you master as it seems you disallowed it.

As you mentioned you were a "beginner", I'll offer additional feedbacks:

• For future PRs (on any repository), it's usually a good idea to create a branch on your repository, so you can allow modifications from targeted repository's maintainers, and also you can more easily work on different PRs in parallel :)
• There were comments about commit hygiene, while they are correct, I'm personally most often looking at the whole diff, if there's not a particular change than I'm interested in, so don't stress about it 😄 (It's a useful thing to research and improve though)

[lukasfri]

@ThierryBerger Thanks! Yeah I haven't dipped into a lot of open source contributing, mainly working on my own stuff so don't know the ins and outs of what people expect from general contributions, thanks for the feedback!