Version 23.08 of the runtime is EOL since the release of 25.08 on September.

Since there are multiple updates to SDL (and others) this will probably require some testing besides just bumping the number at https://github.com/Zelda64Recomp/Zelda64Recomp/blob/dev/flatpak/io.github.zelda64recomp.zelda64recomp.json#L4 and s/llvm18/llvm21/.