Updating python testing as per Yoga testing runtime

Yoga testing runtime[1] has been updated to add py39
testing as voting. Unit tests update are
handled by the job template change in openstack-zuul-job

- https://review.opendev.org/c/openstack/openstack-zuul-jobs/+/820286

this commit makes other required changes in zuul.yaml and
update the classifier in setup.cfg file.

[1] https://governance.openstack.org/tc/reference/runtimes/yoga.html


Change-Id: Ia2caf2508604743cfddbdc76bc520641d1c647d1

.zuul.yaml

@@ -19,7 +19,6 @@
         - openstack-tox-functional-py39:
             required-projects:
               - openstack/placement
-            voting: false
     gate:
       jobs:
         - openstack-tox-functional-py36:
@@ -31,3 +30,6 @@
         - openstack-tox-functional-py38:
             required-projects:
               - openstack/placement
+        - openstack-tox-functional-py39:
+            required-projects:
+              - openstack/placement

setup.cfg

@@ -20,6 +20,7 @@ classifier =
     Programming Language :: Python :: 3.6
     Programming Language :: Python :: 3.7
     Programming Language :: Python :: 3.8
+    Programming Language :: Python :: 3.9
 
 [files]
 packages =

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 minversion = 3.1.1
-envlist = py36,py37,py38,functional,pep8
+envlist = py39,functional,pep8
 skipsdist = true
 # Automatic envs (pyXX) will use the python version appropriate to that
 # env and ignore basepython inherited from [testenv]. That's what we