Make Action Text store_if_blank work for presence validation

Makes this work: https://github.com/rails/rails/pull/52573/files#r1730329576

actiontext/lib/action_text/attribute.rb

@@ -73,7 +73,10 @@ def #{name}=(body)
               if body.present?
                 self.#{name}.body = body
               else
-                self.#{name}.mark_for_destruction if #{name}?
+                if #{name}?
+                  self.#{name}.body = body
+                  self.#{name}.mark_for_destruction
+                end
               end
             end
           CODE

actiontext/test/dummy/app/models/message_without_blanks_with_content_validation.rb

@@ -0,0 +1,3 @@
+class MessageWithoutBlanksWithContentValidation < MessageWithoutBlanks
+  validates :content, presence: true
+end

actiontext/test/unit/model_test.rb

@@ -152,4 +152,16 @@ class ActionText::ModelTest < ActiveSupport::TestCase
       message.update(content: "")
     end
   end
+
+  test "if disallowing blanks, can still validate presence" do
+    message1 = MessageWithoutBlanksWithContentValidation.new(subject: "Greetings", content: "")
+    assert_not_predicate message1, :valid?
+    message1.content = "content"
+    assert_predicate message1, :valid?
+
+    message2 = MessageWithoutBlanksWithContentValidation.new(subject: "Greetings", content: "content")
+    assert_predicate message2, :valid?
+    message2.content = ""
+    assert_not_predicate message2, :valid?
+  end
 end