remove deprecation in dns-debugging-resolution.md

The syntax of this command is deprecated, updated to use the latest format:

```
$ kubectl exec dnsutils cat /etc/resolv.conf
kubectl exec [POD] [COMMAND] is DEPRECATED and will be removed in a future version. Use kubectl kubectl exec [POD] -- [COMMAND] instead.
```

content/en/docs/tasks/administer-cluster/dns-debugging-resolution.md

@@ -56,7 +56,7 @@ Take a look inside the resolv.conf file.
 [Known issues](#known-issues) below for more information)
 
 ```shell
-kubectl exec dnsutils cat /etc/resolv.conf
+kubectl exec -ti dnsutils -- cat /etc/resolv.conf
 ```
 
 Verify that the search path and name server are set up like the following