charm: Test a single bundle to skip flaky tests

Test only on focal-ussuri until flaky tests get fixed.

Change-Id: I4e5121e0c771a78452a98225381ea797168bd753
diff --git a/zuul.d/charm-cinder-storpool-iscsi.yaml b/zuul.d/charm-cinder-storpool-iscsi.yaml
index eff69fb..8cc9082 100644
--- a/zuul.d/charm-cinder-storpool-iscsi.yaml
+++ b/zuul.d/charm-cinder-storpool-iscsi.yaml
@@ -90,6 +90,8 @@
       jobs:
         - zaza-functional-focal-ussuri:
             branches: master
+    experimental:
+      jobs:
         - zaza-functional-focal-ussuri-edge:
             branches: master
         - zaza-functional-focal-wallaby: