Convert all zuul tenants except openstack to Ansible 8

As announced last week [0] we're going to start updating more Zuul
tenants to Ansible 8. This week the plan is to do pyca, pypa, vexxhost,
and nebulous which will result in all tenants except openstack running
Ansible 8 by default.

[0] https://lists.opendev.org/archives/list/service-announce@lists.opendev.org/thread/A7SOKNMQLZXZSTXUI4UOIIGOQHIQSMZ6/

Change-Id: Ib8d336c20dedb26dca5855cb51b4ec8ccb2f48a2

zuul/main.yaml

@@ -86,6 +86,7 @@
 - tenant:
     name: nebulous
     admin-rules: *admin_rules
+    default-ansible-version: '8'
     max-nodes-per-job: 10
     source:
       gerrit:
@@ -1535,6 +1536,7 @@
 - tenant:
     name: vexxhost
     admin-rules: *admin_rules
+    default-ansible-version: '8'
     max-nodes-per-job: 10
     source:
       gerrit:
@@ -1712,6 +1714,7 @@
 - tenant:
     name: pyca
     admin-rules: *admin_rules
+    default-ansible-version: '8'
     max-nodes-per-job: 1
     source:
       gerrit:
@@ -1738,6 +1741,7 @@
 - tenant:
     name: pypa
     admin-rules: *admin_rules
+    default-ansible-version: '8'
     max-nodes-per-job: 1
     source:
       gerrit: