[FIX] web: External Link

In the case of a One2many list view in a `<group>` tag, the 'External
Link' button of a Many2one field (which allows opening the form view) is
not visible.

The `flex: 1 0 auto;` should not be applied in the list view.

Corresponding PR in v12: #28741
opw-1903158

closes odoo/odoo#28812

addons/web/static/src/less/form_view.less

@@ -359,13 +359,13 @@
             }
         }
 
-        :not(.o_row) > .o_field_widget,
+        :not(.o_row):not(.o_data_cell) > .o_field_widget,
         .o_row > .o_field_widget:last-child { // Note: this does not take care
                                               // of an invisible last-child but
                                               // it does not really matter
             // Makes extra buttons (e.g. m2o external button) overflow on the
             // right padding of the parent element
-            .o_input_dropdown {
+            > .o_input_dropdown {
                 .o-flex(1, 0, auto);
             }
         }