[IMP] survey: make error message required when validation is enabled

Before this commit *Validation Error message* was not required for questions
with *Validate Required*. This leads to having `False` displayed if
*Validation Error message* is empty.

With this commit we make *Validation Error message* required for these types
of questions which requires validation. Indeed it makes no sense to required
a validation but having no message explaning why it failed.

closes odoo/odoo#58083

Signed-off-by: Thibault Delavallee (tde) <tde@openerp.com>

addons/survey/views/survey_question_views.xml

@@ -124,7 +124,7 @@
                                             <field name="validation_max_date" attrs="{'invisible': [('question_type', '!=', 'date')]}"/>
                                             <field name="validation_min_datetime" widget="datetime" attrs="{'invisible': [('question_type', '!=', 'datetime')]}"/>
                                             <field name="validation_max_datetime" widget="datetime" attrs="{'invisible': [('question_type', '!=', 'datetime')]}"/>
-                                            <field name="validation_error_msg"/>
+                                            <field name="validation_error_msg" attrs="{'required': [('validation_required', '=', True)]}"/>
                                         </group>
                                     </div>
                                 </div>