Refactor schema_spec.rb for CE-EE parity and simplicity

spec/migrations/active_record/schema_spec.rb

@@ -5,10 +5,10 @@ require 'spec_helper'
 
 describe ActiveRecord::Schema do
   let(:latest_migration_timestamp) do
-    migrations_paths =
-      %w[db ee/db].product(%w[migrate post_migrate]).each_with_object([]) do |migration_dir, memo|
-        memo << Rails.root.join(*migration_dir, '*')
-      end
+    migrations_paths = %w[db ee/db]
+      .product(%w[migrate post_migrate])
+      .map { |path| Rails.root.join(*path, '*') }
+
     migrations = Dir[*migrations_paths]
     migrations.map { |migration| File.basename(migration).split('_').first.to_i }.max
   end