Update use-group-managed-service-accounts.md

CRI 373294317
Customer was receiving error "attempted logon is invalid. This is either due to a bad username or authentication information." and they fixed by adding double quotes on the PluginInput.

It's also something that was trapped on https://msazure.visualstudio.com/CloudNativeCompute/_wiki/wikis/CloudNativeCompute.wiki/190896/Bug-Bash-Windows-gMSA-v2

Author: axelgMS

articles/aks/use-group-managed-service-accounts.md

@@ -160,7 +160,7 @@ credspec:
     HostAccountConfig:
       PluginGUID: '{CCC2A336-D7F3-4818-A213-272B7924213E}'
       PortableCcgVersion: "1"
-      PluginInput: ObjectId=$MANAGED_ID;SecretUri=$SECRET_URI  # SECRET_URI takes the form https://$akvName.vault.azure.net/secrets/$akvSecretName
+      PluginInput: "ObjectId=$MANAGED_ID;SecretUri=$SECRET_URI"  # SECRET_URI takes the form https://$akvName.vault.azure.net/secrets/$akvSecretName
   CmsPlugins:
   - ActiveDirectory
   DomainJoinConfig: