denylist: add luks.cex for centOS

This test requires some magic that only exists on RHCOS s390x builders.
Let's denylist these tests to unblock the pipeline until we fix
cosa to know to ignore centos for this.

Tracking issue coreos#76
See coreos/coreos-assembler#4334

Author: jbtrystram

kola-denylist.yaml

@@ -58,3 +58,11 @@
   tracker: https://github.com/coreos/rhel-coreos-config/issues/70
   osversion:
     - rhel-9.6
+
+# This test won't run on non-rhcos, but kola thinks SCOS is RHCOS
+# See https://github.com/coreos/coreos-assembler/pull/4334
+- pattern: luks.cex
+  tracker: https://github.com/coreos/rhel-coreos-config/issues/76
+  osversion:
+    - centos-9
+    - centos-10