Update runtime to 43 and Oomox to 1.15

[flathubbot]

Started test build 3515

[flathubbot]

Build 3515 successful To test this build, install it from the testing repository:

flatpak install --user https://dl.flathub.org/build-repo/115951/com.github.themix_project.Oomox.flatpakref

[actionless]

thanks! 💯