isolate some tests from settings

Dependencies

• [2] KKMFQDR4 editing source code from within the app
• [3] JMUD7T3O get rid of ugly side-effects in tests

Change contents

• replacement in source.lua at line 337
  [2.176830]→[2.176830:176892](∅→∅)
  − source.set_window_position_from_settings(Settings.source)
  [2.176830]

  [2.176892]
  + if not App.run_tests then

  + source.set_window_position_from_settings(Settings.source)

  + end