Merge branch '46233-rails5-fix-nomethoderror-undefined-method-for-3-string' into 'master'

Resolve "[Rails5] Fix `NoMethodError:  undefined method `-' for "3":String`"

Closes #46233

See merge request gitlab-org/gitlab-ce!18892

lib/gitlab/multi_collection_paginator.rb

@@ -5,7 +5,7 @@ module Gitlab
     def initialize(*collections, per_page: nil)
       raise ArgumentError.new('Only 2 collections are supported') if collections.size != 2
 
-      @per_page = per_page || Kaminari.config.default_per_page
+      @per_page = (per_page || Kaminari.config.default_per_page).to_i
       @first_collection, @second_collection = collections
     end