Enable nova anti-affinity in two-node act-stdby job

Production deployments are recommended to run on active-standby
loadbalancer topology and with nova anti-affinity enabled for higher
level of availability. Job octavia-v2-act-stdby-dsvm-scenario-two-node
will test Octavia under such configuration.

Task: 40413
Story: 2007943

Change-Id: Iab24754bf6881671091a06047767f8b4dc8b5420
diff --git a/zuul.d/jobs.yaml b/zuul.d/jobs.yaml
index 2f94ada..9344eb9 100644
--- a/zuul.d/jobs.yaml
+++ b/zuul.d/jobs.yaml
@@ -570,6 +570,10 @@
       tempest_test_regex: ^octavia_tempest_plugin.tests.scenario.v2
       tox_envlist: all
       devstack_local_conf:
+        post-config:
+            $OCTAVIA_CONF:
+              nova:
+                enable_anti_affinity: True
         test-config:
           "$TEMPEST_CONFIG":
             load_balancer: