Fix the channel value for tang-operator

https://issues.redhat.com/browse/OCPBUGS-25998

Author: mjahoda

modules/nbde-tang-server-operator-installing-cli.adoc

@@ -41,7 +41,7 @@ metadata:
   name: tang-operator
   namespace: openshift-operators
 spec:
-  channel: latest <1>
+  channel: stable <1>
   installPlanApproval: Automatic
   name: tang-operator <2>
   source: redhat-operators <3>