[OVN][CI] Update OVS_BRANCH to be compatible with ovn main

Required since [1].

[1] ovn-org/ovn@4ed71c2

Change-Id: Id8fa2f9dabed8c0bd4d26288fb51012a4c011bba

Author: priteau

zuul.d/base.yaml

@@ -52,7 +52,7 @@
       INSTALL_OVN: True
       OVN_BRANCH: main
       # NOTE(froyo): OVN main branch following OVS stable branch
-      OVS_BRANCH: branch-3.3
+      OVS_BRANCH: branch-3.4
 
 - job:
     name: ovn-octavia-provider-tempest-base
@@ -178,4 +178,4 @@
         INSTALL_OVN: True
         OVN_BRANCH: main
         # NOTE(froyo): OVN main branch following OVS stable branch
-        OVS_BRANCH: branch-3.3
+        OVS_BRANCH: branch-3.4