Add LoginActivity model spec and BrowserDetection concern shared example (#32959)

spec/models/login_activity_spec.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+RSpec.describe LoginActivity do
+  include_examples 'BrowserDetection'
+
+  describe 'Associations' do
+    it { is_expected.to belong_to(:user).required }
+  end
+
+  describe 'Validations' do
+    subject { Fabricate.build :login_activity }
+
+    it { is_expected.to define_enum_for(:authentication_method).backed_by_column_of_type(:string) }
+  end
+end