(MAINT) - TEMP pin to FFI 1.15.2

This change temporarily pins the ffi 1.15.2 gem and pulls this in to be
used in CI for the editor-services.

This change should be temporarily, to resolve failing CI until this bug
is fixed upstream, and released in the next puppet platform release.
See here puppetlabs/puppet#9112

Gemfile

@@ -14,7 +14,7 @@ group :development do
   gem 'puppet-lint', '~> 4.0',            :require => false
   gem 'puppetfile-resolver', '~> 0.6.2',  :require => false
   gem 'yard', '~> 0.9.28',                :require => false
-
+  gem 'ffi', '~> 1.15',                   :require => false
   gem "rubocop", '~> 1.48.1',                          require: false
   gem "rubocop-performance", '~> 1.16',                require: false
   gem "rubocop-rspec", '~> 2.19',                      require: false