Fix CentOS typo (#11161)

The name reported in ansible_distribution is "CentOS", so this could
break some things.

roles/kubernetes/preinstall/vars/main.yml

@@ -97,7 +97,7 @@ pkgs:
           major_versions:
           - "8"
           - "9"
-        Centos: *major_redhat_like
+        CentOS: *major_redhat_like
   rsync: {}
   socat: {}
   software-properties-common: *debian_family_base