Use sequence for unique names on webauthn cred fabricator (#35356)

spec/fabricators/webauthn_credential_fabricator.rb

@@ -4,6 +4,6 @@ Fabricator(:webauthn_credential) do
   user_id { Fabricate(:user).id }
   external_id { Base64.urlsafe_encode64(SecureRandom.random_bytes(16)) }
   public_key { OpenSSL::PKey::EC.generate('prime256v1').public_key }
-  nickname 'USB key'
+  nickname { sequence(:nickname) { |i| "USB Key number #{i}" } }
   sign_count 0
 end