Help Wanted: CI improvements

[ocornut]

Details:

Noting this down. Help greatly wanted if you want to make a PR for this (if you fork you can test CI changes on your fork).

• add SDL3 builds to all platforms. We don't need to build every single combination but we want each backends to be built once, so at least: SDL3, SDLRenderer3, SDL_GPU.
• update Windows CI to use a more recent SDL2
• update Windows CI to use a more recent Vulkan SDK

[ocornut]

Thanks to @scribam for c96e9c8 and 7babc24 !

[ocornut]

Thanks to @yaz0r for #8925. Closing this.