This change ensures that the `GST_EVENT_EOS`,
`GST_EVENT_FLUSH_START` and `GST_EVENT_FLUSH_STOP`
events are forwarded to the sink downstream.
The logging message for `GST_EVENT_FLUSH_START`
has also been fixed.
Part-of: <https://gitlab.freedesktop.org/gstreamer/gstreamer/-/merge_requests/8576>