Fix HTTP 500 on POST /api/v1/admin/ip_blocks (#29308)

spec/models/ip_block_spec.rb

@@ -12,6 +12,8 @@ RSpec.describe IpBlock do
     it { is_expected.to validate_presence_of(:severity) }
 
     it { is_expected.to validate_uniqueness_of(:ip) }
+
+    it { is_expected.to allow_values(:sign_up_requires_approval, :sign_up_block, :no_access).for(:severity) }
   end
 
   describe '#to_log_human_identifier' do