Blacklist libharfbuzz-subset.so.0

[cazfi]

User running on an older system (-> older libharfbuzz) reports this about AppImage generated on newer system (-> newer libharfbuzz-subset):

./Freeciv-gtk4-3.2.2-x86_64.AppImage: symbol lookup error: /tmp/.mount_FreeciNAaoCm/usr/bin/../lib/libharfbuzz-subset.so.0: undefined symbol: hb_free

[probonopd]

Unless an AppImage bundles everything, AppImages only work on newer but not older systems than the build system.

[cazfi]

AppImages only work on newer ... systems than the build system.

I don't think there's guarantees of that either with partially bundled harfbuzz.

[probonopd]

There might be truth in this 😄