tests: multiqueue: fix eos count on test for not-linked case

tests: multiqueue: fix eos count on test for not-linked case

From the test case:

/* This test creates a multiqueue with 2 streams. One receives
 * a constant flow of buffers, the other only gets one buffer, and then
 * new-segment events, and returns not-linked. The multiqueue should not fill.
 */

If one of the queues goes EOS and the other returns NOT_LINKED the stream
can be considerered EOS as a NOT_LINKED means that one of the branches has no
sink downstream that will block the EOS message posting.

https://bugzilla.gnome.org/show_bug.cgi?id=725917