chore: € character at article model TITLE_CHARACTERS_ALLOWED (#17790)

app/models/article.rb

@@ -83,6 +83,7 @@ class Article < ApplicationRecord
     \u303d        # Either a line chart plummeting or the letter M, not sure
     \u3297        # Circled Ideograph Congratulation
     \u3299        # Circled Ideograph Secret
+    \u20ac        # Euro symbol (€)
     \u{1f000}-\u{1ffff} # More common emoji
   ]+/m
   # rubocop:enable Lint/DuplicateRegexpCharacterClassElement

spec/models/article_spec.rb

@@ -237,6 +237,14 @@ RSpec.describe Article, type: :model do
         expect(article.title).to eq allowed_title
       end
 
+      it "allows Euro symbol (€)" do
+        allowed_title = "Euro code €€€"
+
+        article = create(:article, title: allowed_title)
+
+        expect(article.title).to eq allowed_title
+      end
+
       it "produces a proper title" do
         test_article = build(:article, title: "An Article Title")