bluetooth/gst: Use bin instead of pipeline

A pipeline is effectively a bin, with all kinds of (currently unused)
bits attached.
3 jobs for gst-synchronous in 7 minutes and 26 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Container
passed #7029421
build-container

00:00:25

 
  Build
passed #7029422
build-autotools

00:07:00

passed #7029423
build-meson

00:01:03