syncthing: Usage reporting form is still shown on buster

In stable container, the functional test test_add_a_syncthing_folder is failing. This is because the "Allow Anonymous Usage Reporting?" form is shown, and waiting for user input.

In testing container, the form is not shown, it is skipped due to these changes: 77face68

So these changes do not work as intended on buster (which could be fine). But the problem is that the functional test case was also changed, under the assumption that the usage reporting box would not be shown.