Inform Arel we don't need additional type casting in tests

Part of the larger refactoring to remove type casting from Arel. We can
inform it that we already have the right type by wrapping the value in
an `Arel::Nodes::Quoted`. This commit can be reverted when we have
removed type casting from Arel in Rail 5.1

activerecord/test/cases/relation/merging_test.rb

@@ -25,8 +25,8 @@ def test_relation_to_sql
   end
 
   def test_relation_merging_with_arel_equalities_keeps_last_equality
-    devs = Developer.where(Developer.arel_table[:salary].eq(80000)).merge(
-      Developer.where(Developer.arel_table[:salary].eq(9000))
+    devs = Developer.where(Developer.arel_table[:salary].eq(Arel::Nodes::Quoted.new(80000))).merge(
+      Developer.where(Developer.arel_table[:salary].eq(Arel::Nodes::Quoted.new(9000)))
     )
     assert_equal [developers(:poor_jamis)], devs.to_a
   end

activerecord/test/cases/relation/where_chain_test.rb

@@ -43,7 +43,7 @@ def test_not_in
     end
 
     def test_association_not_eq
-      expected = Comment.arel_table[@name].not_eq('hello')
+      expected = Comment.arel_table[@name].not_eq(Arel::Nodes::Quoted.new('hello'))
       relation = Post.joins(:comments).where.not(comments: {title: 'hello'})
       assert_equal(expected.to_sql, relation.where_values.first.to_sql)
     end

activerecord/test/models/author.rb

@@ -34,7 +34,7 @@ def ratings
            -> { where(title: 'Welcome to the weblog').where('comments_count = ?', 1) },
            class_name: 'Post'
   has_many :welcome_posts_with_comments,
-           -> { where(title: 'Welcome to the weblog').where(Post.arel_table[:comments_count].gt(0)) },
+           -> { where(title: 'Welcome to the weblog').where(Post.arel_table[:comments_count].gt(Arel::Nodes::Quoted.new(0))) },
            class_name: 'Post'
 
   has_many :comments_desc, -> { order('comments.id DESC') }, :through => :posts, :source => :comments