Merge tag '4.2.0' into debian/xena

oslo.serialization 4.2.0 release

meta:version: 4.2.0
meta:diff-start: -
meta:series: xena
meta:release-type: release
meta:pypi: yes
meta:first: yes
meta:release:Author: Hervé Beraud <hberaud@redhat.com>
meta:release:Commit: Hervé Beraud <hberaud@redhat.com>
meta:release:Change-Id: I946c734c8958b641e211453289d7bb3f26bb9700
meta:release:Code-Review+2: Hervé Beraud <herveberaud.pro@gmail.com>
meta:release:Code-Review+2: Thierry Carrez <thierry@openstack.org>
meta:release:Workflow+1: Thierry Carrez <thierry@openstack.org>