gha: enable IPv6 in clustermesh upgrade/downgrade workflow

[ upstream commit dbe56dd ]

Now that known issues causing connection disruption (which appeared to
mostly affect dual stack clusters) have been fixed, let's enable IPv6
again in the clustermesh upgrade/downgrade workflow.

Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>
Signed-off-by: Marco Iorio <marco.iorio@isovalent.com>

.github/workflows/tests-clustermesh-upgrade.yaml

@@ -118,9 +118,6 @@ jobs:
           "
 
           # * bpf.masquerade is disabled due to #23283
-          # * IPv6 is disabled because an issue under investigation seems to
-          #   possibly cause seldom and brief connection disruptions on agent
-          #   restart in dual stack clusters, independently of clustermesh.
           # * Hubble is disabled to avoid the performance penalty in the testing
           #   environment due to the relatively high traffic load.
           CILIUM_INSTALL_DEFAULTS=" \
@@ -130,7 +127,7 @@ jobs:
             --set=hubble.enabled=false \
             --set=tunnel=vxlan \
             --set=ipv4.enabled=true \
-            --set=ipv6.enabled=false \
+            --set=ipv6.enabled=true \
             --set=clustermesh.useAPIServer=true \
             --set=clustermesh.config.enabled=true"