Remove body_as_json in favor of built-in response.parsed_body for JSON response specs (#31749)

spec/requests/api/v1/preferences_spec.rb

@@ -34,7 +34,7 @@ RSpec.describe 'Preferences' do
         expect(response)
           .to have_http_status(200)
 
-        expect(body_as_json)
+        expect(response.parsed_body)
           .to be_present
       end
     end