Load MiniMagick before use

We only reference MiniMagick when rescuing errors but when it's not
loaded, that code fails to find the error class itself to apply the
rescue block.

The rescue block is covered by a spec but the code passes there as
MiniMagick is loaded.

We can see this error only in development, staging and production.

app/models/enterprise.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: false
 
+require "mini_magick"
+
 class Enterprise < ApplicationRecord
   SELLS = %w(unspecified none own any).freeze
   ENTERPRISE_SEARCH_RADIUS = 100

app/models/spree/image.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "mini_magick"
+
 module Spree
   class Image < Asset
     has_one_attached :attachment, service: image_service do |attachment|