Fix Appraisals requiring ruby-vips

[nickcharlton]

This started being required, but wasn't included for these Appraisals which meant they all started failing.

[nickcharlton]

Bundler::GemRequireError:
  There was an error while trying to load the gem 'ruby-vips'.
  Gem Load Error is: Could not open library 'vips.so.42': vips.so.42: cannot open shared object file: No such file or directory.
  Could not open library 'libvips.so.42': libvips.so.42: cannot open shared object file: No such file or directory.

Sigh. Looks like we need it in the container as well.

[nickcharlton]

Installing libvips-dev into the container worked, but now there's an extra step only for Appraisals. These have a habit of hanging around, but we'll just need to rely on eventually discovering it's not needed.