Add fontconfig to prevent crashing

[yosifkit]

Sharp v0.34.2 is the version used by Ghost v5 and v6, hence the version in the link.

Fixes https://github.com/docker-library/ghost/issues/453

[tianon]

I think it would be useful if we could reproduce the failure (https://github.com/docker-library/ghost/issues/453#issuecomment-3403773603) before we merge the fix, so we can be sure this really does fix it. :sweat_smile:

[yosifkit]

Size change for reference:

root@b511a921aa84:/var/lib/ghost# apt-get install --no-install-recommends fontconfig
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
The following additional packages will be installed:
  fontconfig-config fonts-dejavu-core libbrotli1 libexpat1 libfontconfig1 libfreetype6 libpng16-16
The following NEW packages will be installed:
  fontconfig fontconfig-config fonts-dejavu-core libbrotli1 libexpat1 libfontconfig1 libfreetype6 libpng16-16
0 upgraded, 8 newly installed, 0 to remove and 0 not upgraded.
Need to get 3266 kB of archives.
After this operation, 7328 kB of additional disk space will be used.
Do you want to continue? [Y/n]

[yosifkit]

Just pushed a rebase on #456. I think we still need a reproducer to know if this is necessary.