docs: add flow combiner ref/unref to docs
So new-in-1.12 index actually has some entries.
diff --git a/docs/libs/gstreamer-libs-sections.txt b/docs/libs/gstreamer-libs-sections.txt
index 515eb76..42adf5b 100644
--- a/docs/libs/gstreamer-libs-sections.txt
+++ b/docs/libs/gstreamer-libs-sections.txt
@@ -839,6 +839,8 @@
GstFlowCombiner
gst_flow_combiner_new
gst_flow_combiner_free
+gst_flow_combiner_ref
+gst_flow_combiner_unref
gst_flow_combiner_update_flow
gst_flow_combiner_add_pad
gst_flow_combiner_remove_pad