[FIX] base_tier_validation: last comment instead of first comment

- With multiple approbation, the first comment is repeated into
mail.message and propagate wrong message

base_tier_validation/models/tier_validation.py

@@ -404,7 +404,7 @@ def _notify_rejected_review_body(self):
             lambda r: (self.env.user in r.reviewer_ids) and r.comment
         )
         if has_comment:
-            comment = has_comment.mapped("comment")[0]
+            comment = has_comment.mapped("comment")[-1]
             return _("A review was rejected by %(user)s. (%(comment)s)") % {
                 "user": self.env.user.name,
                 "comment": comment,