Windows: SDL2 to 2.24.0, SDL2_mixer to 2.6.2, SDL2_ttf to 2.20.1, SDL_image to 2.6.2

[misl6]

Windows:

• Bumps SDL2 to 2.24.0 (the same pinned in kivy/kivy for macOS and Linux wheels)
• Bumps SDL2_mixer to 2.6.2 (the same pinned in kivy/kivy for macOS and Linux wheels)
• Bumps SDL2_ttf to 2.20.1 (the same pinned in kivy/kivy for macOS and Linux wheels)
• Bumps SDL_image to 2.6.2 (the same pinned in kivy/kivy for macOS and Linux wheels)
• Bumps kivy_deps.sdl2_dev and kivy_deps.sdl2 to 0.4.6

PS: git://github.com/kivy/kivy.git was failing.

⚠️ When merging into master, we should add [publish sdl2 win] into the commit message.