Update _help.py

Change mention of `CBLMariner` to `AzureLinux` in `--os-sku` description.

Author: jakjang

src/azure-cli/azure/cli/command_modules/acs/_help.py

@@ -91,7 +91,7 @@
       - "`az aks get-versions`"
   - name: --os-sku
     type: string
-    short-summary: The OS SKU of the agent node pool. Ubuntu or CBLMariner.
+    short-summary: The OS SKU of the agent node pool. Ubuntu or AzureLinux.
   - name: --ssh-key-value
     type: string
     short-summary: Public key path or key contents to install on node VMs for SSH access. For example, 'ssh-rsa AAAAB...snip...UcyupgH azureuser@linuxvm'.