[FIX] survey: Unescape characters in mail subject

To reproduce the error:
Create a survey (title must contain ") and send it

Error:
The mail subject is incorrect: the character " is replaced with "

OPW-2536206

X-original-commit: 37cea37

addons/survey/wizard/survey_invite.py

@@ -210,7 +210,7 @@ def _get_answers_values(self):
 
     def _send_mail(self, answer):
         """ Create mail specific for recipient containing notably its access token """
-        subject = self.env['mail.render.mixin']._render_template(self.subject, 'survey.user_input', answer.ids, post_process=True)[answer.id]
+        subject = self.env['mail.render.mixin'].with_context(safe=True)._render_template(self.subject, 'survey.user_input', answer.ids, post_process=True)[answer.id]
         body = self.env['mail.render.mixin']._render_template(self.body, 'survey.user_input', answer.ids, post_process=True)[answer.id]
         # post the message
         mail_values = {