Use zlib compression for now

[smoogipoo]

Fixes ppy/osu#30175

I know how this looks, but this is actually zlib: https://github.com/plougher/squashfs-tools/blob/cc41bf6a92f3b474b392dd5cb6d7066243800a4e/squashfs-tools/compressor.c#L32-L34

(home) ~/Desktop $ dd if=old.AppImage bs=1 skip=$(./old.AppImage --appimage-offset) count=32 2>/dev/null | file -
/dev/stdin: Squashfs filesystem, little endian, version 4.0, zlib compressed, 0 bytes, 478 inodes, blocksize: 131072 bytes, created: Thu Jan  1 00:00:00 1970
(home) ~/Desktop $ dd if=new.AppImage bs=1 skip=$(./new.AppImage --appimage-offset) count=32 2>/dev/null | file -
/dev/stdin: Squashfs filesystem, little endian, version 4.0, zstd compressed, 0 bytes, 472 inodes, blocksize: 131072 bytes, created: Thu Jan  1 00:00:00 1970
(home) ~/Desktop $ dd if=new2.AppImage bs=1 skip=$(./new2.AppImage --appimage-offset) count=32 2>/dev/null | file -
/dev/stdin: Squashfs filesystem, little endian, version 4.0, zlib compressed, 0 bytes, 471 inodes, blocksize: 131072 bytes, created: Thu Jan  1 00:00:00 1970

old = 2024.817.0 (pre-velopack)
new = 2024.1009.1 (pulled)
new2 = this PR

Have tested that this works for me, and am confident given it matches the old compression.