Use pluck on DomainAllow.allowed_domains for export (#36019)

spec/models/domain_allow_spec.rb

@@ -12,4 +12,19 @@ RSpec.describe DomainAllow do
       it { is_expected.to_not allow_value('xn--r9j5b5b').for(:domain) }
     end
   end
+
+  describe '.allowed_domains' do
+    subject { described_class.allowed_domains }
+
+    context 'without domain allows' do
+      it { is_expected.to be_an(Array).and(be_empty) }
+    end
+
+    context 'with domain allows' do
+      let!(:allowed_domain) { Fabricate :domain_allow }
+      let!(:other_allowed_domain) { Fabricate :domain_allow }
+
+      it { is_expected.to contain_exactly(allowed_domain.domain, other_allowed_domain.domain) }
+    end
+  end
 end