Original commit message from CVS:
* codegen/argtypes.py:
Add handling of 'keep-refcount' for GBoxed arguments.
* gst/gst.defs:
Mark the appropriate 'gst_message_new_*' arguments when the method
takes the ownership of the passed gst.Structure/gst.TagList
* testsuite/test_message.py:
Test for creating messages that take a gst.Structure/gst.TagList as
argument and make sure they're properly created.
Fixes #556054