restricted: Fix pd migration from erp5 to wendelin

When cleaning up Wendelin from restricted python pandas code
(see https://lab.nexedi.com/levin.zimmermann/wendelin/tree/remove-redundant-pandas),
it turned out that there was one line still missing in erp5.
This missing line caused a failed test in wendelin functional tests:

  https://erp5js.nexedi.net/#/test_result_module/20220614-1B46817BD/6

Readding the line fixed the test.