oslo.serialization 5.9.0 release

meta:version: 5.9.0
meta:team: oslo
meta:diff-start: -
meta:series: gazpacho
meta:branch: master
meta:release-type: release
meta:pypi: yes
meta:first: yes
meta:release:Author: Stephen Finucane <sfinucan@redhat.com>
meta:release:Commit: Stephen Finucane <sfinucan@redhat.com>
meta:release:Change-Id: I6b1469c6f51218b4aed5685768d2283e39cedde3
meta:release:Code-Review+2: Elod Illes <elod.illes@est.tech>
meta:release:Workflow+1: Thierry Carrez <thierry@openstack.org>
meta:release:Code-Review+2: Thierry Carrez <thierry@openstack.org>
meta:release:Code-Review+1: Takashi Kajinami <kajinamit@oss.nttdata.com>