When updating article scores, use new score for blackbox (#13009)

Fixes #13008

Add a test case for blackbox stability

This failed as expected on master and passed on this branch, when a
reaction (which would change the article's calculated score during
update) is added, the hotness should be stable, and not modified
during the second call to `#update_score`.

app/models/article.rb

@@ -375,8 +375,8 @@ class Article < ApplicationRecord
   end
 
   def update_score
-    new_score = reactions.sum(:points) + Reaction.where(reactable_id: user_id, reactable_type: "User").sum(:points)
-    update_columns(score: new_score,
+    self.score = reactions.sum(:points) + Reaction.where(reactable_id: user_id, reactable_type: "User").sum(:points)
+    update_columns(score: score,
                    comment_score: comments.sum(:score),
                    hotness_score: BlackBox.article_hotness_score(self),
                    spaminess_rating: BlackBox.calculate_spaminess(self))

spec/models/article_spec.rb

@@ -1008,4 +1008,13 @@ RSpec.describe Article, type: :model do
       expect(article.plain_html).not_to include("highlight__panel")
     end
   end
+
+  describe "#update_score" do
+    it "stably sets the correct blackbox values" do
+      create(:reaction, reactable: article, points: 1)
+
+      article.update_score
+      expect { article.update_score }.not_to change { article.reload.hotness_score }
+    end
+  end
 end