fix: alteration of loop while iterating over it

mail_client/mail_client/doctype/outgoing_mail/outgoing_mail.py

@@ -524,7 +524,7 @@ def _update_recipients(self, type: str, recipients: list[str] | None = None) ->
 			if d not in prev_recipients:
 				self._add_recipient(type, d)
 
-		for d in self.recipients:
+		for d in self.recipients[:]:
 			if d.type == type and d.email not in recipients:
 				self.recipients.remove(d)