CI: added ccache to appimage build workflow

[pflyly]

see the test run here: https://github.com/pflyly/ppsspp/actions/runs/15567591425

build time from ~10m to ~1m16s

[pflyly]

Hi!
I noticed that the current appimage in the releases is significantly smaller and doesn't work. I think you should rebuild it again, I think archlinux updating to llvm20 messed something up back then.

[anr2me]

Hi! I noticed that the current appimage in the releases is significantly smaller and doesn't work. I think you should rebuild it again, I think archlinux updating to llvm20 messed something up back then.

Yeah, it's strange that the x86_64 AppImage to be smaller than the aarch64 AppImage, it's usually larger because aarch64 doesn't have the vulkan-intel package.

Should we re-run the job? 🤔