Prepare new stable/yoga release

This is a convenience patch related to convenience releases proposed
recently [1].

[1] https://review.opendev.org/q/topic:yoga-convenience-before-em

Change-Id: I935c31dbe166bff8cac2335da6471c29755df3c6

metadata.json

@@ -63,5 +63,5 @@
     ],
     "source": "https://opendev.org/openstack/puppet-tempest.git",
     "summary": "Puppet module for OpenStack Tempest",
-    "version": "20.3.0"
+    "version": "20.4.0"
 }