stream.py: cast memoryview to bytes as from_buffer() methods do not handle this case

gstlal/python/stream.py

@@ -374,7 +374,12 @@ class Stream(ElementRegistry):
 				success, mapinfo = memory.map(Gst.MapFlags.READ)
 				assert success
 				if mapinfo.data:
-					rows = cls._caps_buffer_map[caps.to_string()](mapinfo.data)
+					# FIXME: gst-python 1.18 returns a memoryview
+					# instead of a read-only bytes-like object, so
+					# cast to bytes. this is likely inefficient but
+					# a proper solution will require .from_buffer()
+					# to leverage the buffer protocol instead
+					rows = cls._caps_buffer_map[caps.to_string()](bytes(mapinfo.data))
 					data.extend(rows)
 
 				memory.unmap(mapinfo)