Fix SDL_EventFilter defintions for GCC 14

[duelafn]

GCC 14 enables -Werror=incompatible-pointer-types which results in expected 'SDL_EventFilter' {aka 'int (*)(void *, SDL_Event *)'} but argument is of type 'int (**)(void *, SDL_Event *)' errors in the call to SDL_SetEventFilter.

The kivy EventFilter definitions didn't exactly match the SDL definitions at [1] and [2]. This patch updates the kivy definitions to match the SDL definitions.

This partially addresses #8557

[1] https://wiki.libsdl.org/SDL2/SDL_EventFilter [2] https://wiki.libsdl.org/SDL2/SDL_SetEventFilter

Maintainer merge checklist

• [ ] Title is descriptive/clear for inclusion in release notes.
• [ ] Applied a Component: xxx label.
• [ ] Applied the api-deprecation or api-break label.
• [ ] Applied the release-highlight label to be highlighted in release notes.
• [ ] Added to the milestone version it was merged into.
• [ ] Unittests are included in PR.
• [ ] Properly documented, including versionadded, versionchanged as needed.