Update HCOVersion to 4.17.21

Author: cnv-bot-axuba

_attributes/common-attributes.adoc

@@ -106,7 +106,7 @@ endif::[]
 //openshift virtualization (cnv)
 :VirtProductName: OpenShift Virtualization
 :VirtVersion: 4.17
-:HCOVersion: 4.17.7
+:HCOVersion: 4.17.21
 :CNVNamespace: openshift-cnv
 :CNVOperatorDisplayName: OpenShift Virtualization Operator
 :CNVSubscriptionSpecSource: redhat-operators