ci: linux: Freeze AppImage binaries

A regression was introduced on May 13 by linuxdeploy that causes file
open dialogs to crash yuzu in the AppImage (likely this commit
1e28ee38fa174279defe70cdaadf2a552c80258c from
linuxdeploy/linuxdeploy-desktopfile). Instead of downloading the latest
version from each of the repos we use to build the AppImage, just
download the ones hosted at yuzu-emu/ext-linux-bin, which are the same
binaries we have been using, but verified to be working and won't update
on us beyond our control.

This can eventually be moved into the container itself to remove the
need to download them at build time.