Building new records with enum scopes now works as expected

Previously, this would give an `ArgumentError`:

   class Issue < ActiveRecord::Base
     enum :status, [:open, :finished]
   end

   Issue.open.build # => ArgumentError: '0' is not a valid status
   Issue.open.create # => ArgumentError: '0' is not a valid status

PR #13542 muted the error, but the issue remains. This commit fixes
the issue by allowing the enum value to be written directly via the
setter:

   Issue.new.status = 0 # This now sets status to :open

Assigning a value directly via the setter like this is not part of the
documented public API, so users should not rely on this behavior.

Closes #13530.

activerecord/lib/active_record/enum.rb

@@ -72,10 +72,16 @@ def enum(definitions)
         _enum_methods_module.module_eval do
           # def status=(value) self[:status] = STATUS[value] end
           define_method("#{name}=") { |value|
-            unless enum_values.has_key?(value) || enum_values.has_value?(value) || value.blank?
+            if enum_values.has_key?(value)|| value.blank?
+              self[name] = enum_values[value]
+            elsif enum_values.has_value?(value)
+              # Assigning a value directly is not a end-user fetaure, hence it's not documented.
+              # This is used internally to make building objects from the generated scopes work
+              # as expected, i.e. +Conversation.archived.build.archived?+ should be true.
+              self[name] = value
+            else
               raise ArgumentError, "'#{value}' is not a valid #{name}"
             end
-            self[name] = enum_values[value]
           }
 
           # def status() STATUS.key self[:status] end

activerecord/test/cases/enum_test.rb

@@ -79,12 +79,13 @@ class EnumTest < ActiveRecord::TestCase
     assert_equal 2, Book::STATUS[:published]
   end
 
-  test "first_or_initialize with enums' scopes" do
-    class Issue < ActiveRecord::Base
-      enum status: [:open, :closed]
-    end
+  test "building new objects with enum scopes" do
+    assert Book.written.build.written?
+    assert Book.read.build.read?
+  end
 
-    assert Issue.open.empty?
-    assert Issue.open.first_or_initialize
+  test "creating new objects with enum scopes" do
+    assert Book.written.create.written?
+    assert Book.read.create.read?
   end
 end

activerecord/test/schema/schema.rb

@@ -327,10 +327,6 @@ def create_table(*args, &block)
     t.string     :color
   end
 
-  create_table :issues, force: true do |t|
-    t.integer :status
-  end
-
   create_table :items, force: true do |t|
     t.column :name, :string
   end