Standardize uniqueness validation declaration on `Mention` (#33247)

app/models/mention.rb

@@ -18,7 +18,7 @@ class Mention < ApplicationRecord
 
   has_one :notification, as: :activity, dependent: :destroy
 
-  validates :account, uniqueness: { scope: :status }
+  validates :account_id, uniqueness: { scope: :status_id }
 
   scope :active, -> { where(silent: false) }
   scope :silent, -> { where(silent: true) }

spec/models/mention_spec.rb

@@ -3,8 +3,14 @@
 require 'rails_helper'
 
 RSpec.describe Mention do
-  describe 'validations' do
+  describe 'Associations' do
     it { is_expected.to belong_to(:account).required }
     it { is_expected.to belong_to(:status).required }
   end
+
+  describe 'Validations' do
+    subject { Fabricate.build :mention }
+
+    it { is_expected.to validate_uniqueness_of(:account_id).scoped_to(:status_id) }
+  end
 end