tests: Fix backgroundsource test
tests: Fix backgroundsource test

pitivi/gst-editing-services,volodymyrrudyi/gst-editing-services,pitivi/gst-editing-services,cfoch/gst-editing-services,cfoch/gst-editing-services,cfoch/gst-editing-services,volodymyrrudyi/gst-editing-services,pitivi/gst-editing-services,volodymyrrudyi/gst-editing-services,cfoch/ges,cfoch/gst-editing-services,cfoch/ges,cfoch/ges,pitivi/gst-editing-services,cfoch/ges