Use Py_TPFLAGS_HAVE_GC for Row

Use Py_TPFLAGS_HAVE_GC for Row

Fixed an issue in the C extension for the :class:`_result.Row` class which
could lead to a memory leak in the unlikely case of a :class:`_result.Row`
object which referred to an ORM object that then was mutated to refer back
to the ``Row`` itself, creating a cycle. The Python C APIs for tracking GC
cycles has been added to the native :class:`_result.Row` implementation to
accommodate for this case.

Fixes: #5348
Change-Id: I3ac32012f29fbb59f8921cf2a124fa3a7ac5f0d1