tests: flvmux: Fix pushing invalid audio caps in tests
tests: flvmux: Fix pushing invalid audio caps in tests

Previous commit created caps with incorrect aac codec data
that did not match the audio channel.

https://bugzilla.gnome.org/show_bug.cgi?id=797256

GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good,pexip/gst-plugins-good,GStreamer/gst-plugins-good,pexip/gst-plugins-good