Fix: extract mentions when publishing cards

This wasn't working when creation and publishing happened on separated instances
of the same record, which is what happens when you edit a draft and then you
publish it

https://app.fizzy.do/5986089/cards/2835/edit

app/models/card/mentions.rb

@@ -7,5 +7,9 @@ module Card::Mentions
     def mentionable?
       published?
     end
+
+    def should_check_mentions?
+      saved_change_to_status? && published?
+    end
   end
 end

app/models/concerns/mentions.rb

@@ -49,7 +49,7 @@ module Mentions
     end
 
     def should_create_mentions?
-      mentionable? && mentionable_content_changed?
+      mentionable? && (mentionable_content_changed? || should_check_mentions?)
     end
 
     def mentionable_content_changed?
@@ -64,4 +64,8 @@ module Mentions
     def mentionable?
       true
     end
+
+    def should_check_mentions?
+      false
+    end
 end

test/models/concerns/mentions_test.rb

@@ -20,6 +20,8 @@ class MentionsTest < ActiveSupport::TestCase
         boards(:writebook).cards.create title: "Cleanup", description: "Did you finish up with the cleanup, @david?"
       end
 
+      card = Card.find(card.id)
+
       assert_difference -> { Mention.count }, +1 do
         card.published!
       end
@@ -33,6 +35,8 @@ class MentionsTest < ActiveSupport::TestCase
         boards(:writebook).cards.create title: "Cleanup", description: "Did you finish up with the cleanup, #{attachment.to_html}?"
       end
 
+      card = Card.find(card.id)
+
       assert_difference -> { Mention.count }, +1 do
         card.published!
       end