Confirm from email always not valid when updating "online registration" of an event after updating to 5.20.2
After updating from 5.19 to 5.20.2 the "online registration" tab of an event cannot be updated because the "Confirm From Email" is always invalid.
- Save the "online registration" form of an existing event https://www.example.com/en/civicrm/event/manage/registration?reset=1&action=update&id=xxx with a valid "Confirm from email"
- Got an error "Confirm From Email", "Email is not valid" Full error in the logs: /civicrm/event/manage/registration?action=update&id=xx&component=event&qfKey=xx&snippet=json Notice: Use of undefined constant INTL_IDNA_VARIANT_UTS46 - assumed 'INTL_IDNA_VARIANT_UTS46' in HTML_QuickForm_Rule_Email->validate() (line 58 of /sites/all/modules/civicrm/packages/HTML/QuickForm/Rule/Email.php) Warning: idn_to_ascii() expects parameter 3 to be integer, string given in HTML_QuickForm_Rule_Email->validate() (line 58 of /sites/all/modules/civicrm/packages/HTML/QuickForm/Rule/Email.php).
Using php 7.1 with php-intl