Fix py38 jobs by using focal rather than jammy

Related to https://lists.openstack.org/pipermail/openstack-discuss/2023-February/032247.html

Change-Id: Icf66914c2b5b6221e55595c01d018617b224c6ea

.zuul.yaml

@@ -13,6 +13,7 @@
 - job:
     name: cross-nova-tox-py38
     parent: openstack-tox
+    nodeset: ubuntu-focal
     description: |
       Run cross-project unit tests on nova.
     vars:
@@ -25,6 +26,7 @@
 - job:
     name: cross-neutron-tox-py38
     parent: openstack-tox
+    nodeset: ubuntu-focal
     description: |
       Run cross-project unit tests on neutron.
     timeout: 3600
@@ -39,7 +41,7 @@
     templates:
       - check-requirements
       - lib-forward-testing-python3
-      - openstack-python3-antelope-jobs
+      - openstack-python3-jobs
       - periodic-stable-jobs
       - publish-openstack-docs-pti
       - release-notes-jobs-python3