Extract TEXT_LENGTH_LIMIT constant in Appeal class (#30638)

spec/models/appeal_spec.rb

@@ -3,6 +3,19 @@
 require 'rails_helper'
 
 describe Appeal do
+  describe 'Validations' do
+    it 'validates text length is under limit' do
+      appeal = Fabricate.build(
+        :appeal,
+        strike: Fabricate(:account_warning),
+        text: 'a' * described_class::TEXT_LENGTH_LIMIT * 2
+      )
+
+      expect(appeal).to_not be_valid
+      expect(appeal).to model_have_error_on_field(:text)
+    end
+  end
+
   describe 'scopes' do
     describe 'approved' do
       let(:approved_appeal) { Fabricate(:appeal, approved_at: 10.days.ago) }