SDL2_image: update to 2.8.12; SDL3_image: update to 3.4.4

[Rutpiv]

Testing the changes

• I tested the changes in this PR: briefly

Local build testing

• I built this PR locally for my native architecture (x86_64)
• I built this PR locally for these architectures using specific masterdirs:
  • x86_64-musl
  • i686
• I built this PR locally for these architectures (crossbuilds):
  • aarch64
  • aarch64-musl
  • armv7l
  • armv7l-musl
  • armv6l
  • armv6l-musl

[Rutpiv]

CI keeps failing on fetch issues unrelated to this PR (dependency fetch on armv7l previously, source fetch on aarch64-musl now). Builds fine locally across all tested architectures; a restart should clear it.