Fatal error due to removed function CRM_Core_OptionGroup::getLabel()

Submitting a grant application with custom data fails because there is a call to CRM_Core_OptionGroup::getLabel() in CRM_Grant_BAO_GrantApplicationPage::sendMail().

This function has long been deprecated in favour of CRM_Core_PseudoConstant::getLabel() and was removed in https://github.com/civicrm/civicrm-core/commit/ff8d01ebdf58a8c6cecb65b4dce3fa550e431f3c.