[FIX] hr_holidays: fix email template subject error

Currently, In TimeOff module If we schedule activity for leave to defer
in the subject of email we see some extra non-ascii characters.
because emails subject lines contains non ASCII characters so they can
not encoded.

So in this commit, replace the arrow sign by slash(/) between two dates
in name_get.

closes odoo/odoo#70416

Taskid: 2501374
Signed-off-by: Yannick Tivisse (yti) <yti@odoo.com>

addons/hr_holidays/models/hr_leave.py

@@ -691,7 +691,7 @@ class HolidaysRequest(models.Model):
                 else:
                     display_date = fields.Date.to_string(leave.date_from)
                     if leave.number_of_days > 1:
-                        display_date += ' ⇨ %s' % fields.Date.to_string(leave.date_to)
+                        display_date += ' / %s' % fields.Date.to_string(leave.date_to)
                     if self.env.context.get('hide_employee_name') and 'employee_id' in self.env.context.get('group_by', []):
                         res.append((
                             leave.id,