Make test dependencies conditional so we can enable them when running autopkgtest

--- a/Gemfile
+++ b/Gemfile
@@ -324,7 +324,7 @@
   gem 'raindrops', '~> 0.18'
 end
 
-group :development, :test do
+if ENV["INCLUDE_TEST_DEPENDS"] == "true"
   gem 'bullet', '~> 6.0.2'
   gem 'pry-byebug', '~> 3.5','>= 3.5.1', platform: :mri
   gem 'pry-rails', '~> 0.3.9'
@@ -355,9 +355,6 @@
   gem 'png_quantizator', '~> 0.2.1', require: false
 
   gem 'parallel', '~> 1.19', require: false
-end
-
-group :test do
   gem 'fuubar', '~> 2.2'
   gem 'rspec-retry', '~> 0.6.1'
   gem 'rspec_profiling', '~> 0.0.5'