valve: Fix unit test by sending caps before buffers
valve: Fix unit test by sending caps before buffers

Unexpected critical/warning: gstpad.c:4400:gst_pad_push_data:<'':src> Got data flow before segment event

https://bugzilla.gnome.org/show_bug.cgi?id=763753

StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer,StreamUtils/gstreamer