Update libvips to 8.15.2

[littleforest]

See notes on #49

[brandoncc]

Has this been tested in a deployed application? I just put up a PR that adds heroku-24 support and also upgrades to libvips 8.17.3 and I had to build libarchive in the heroku-22 Dockerfile. Heroku claims that libarchive is already installed on heroku-22, but require 'vips' failed when I only did what you have done in this PR.

Loading production environment (Rails 8.1.1)
myapp(prod):001> Vips::Image
(myapp):1:in '<main>': uninitialized constant Vips::Image (NameError)
myapp(prod):002> require 'vips'
(myapp):2:in '<main>': Could not open library 'vips.so.42': vips.so.42: cannot open shared object file: No such file or directory. (LoadError)
Could not open library 'libvips.so.42': libarchive.so.13: cannot open shared object file: No such file or directory.
Searched in <system library path>

I've successfully run require 'vips' on both heroku-22 and heroku-24 with the buildpack in #58.

[thoughtbot-github]

Hi @brandoncc, thank you for the notes! The PR author is no longer with the team, and we don't have further context easily, but we can pick this back up if Dave prioritizes it for us :)