[REF] Fix new checks of latest version of flake8

firstname_display_name_trigger/res_partner.py

@@ -65,7 +65,8 @@ class ResPartner(orm.Model):
 
     # indirection to avoid passing a copy of the overridable method when
     # declaring the function field
-    _display_name = lambda self, *a, **kw: self._display_name_compute(*a, **kw)
+    def _display_name(self, *a, **kw):
+        return self._display_name_compute(*a, **kw)
 
     _columns = {
         # extra field to allow ORDER BY to match visible names