Update New-AzApplicationGatewayFirewallPolicyManagedRuleSet.md (#18972)

Typo in example command

Author: shiftychris

src/Network/Network/help/New-AzApplicationGatewayFirewallPolicyManagedRuleSet.md

@@ -26,7 +26,7 @@ The **New-AzApplicationGatewayFirewallPolicyManagedRuleSet** creates a managed-r
 ### Example 1
 ```powershell
 $managedRuleSet = New-AzApplicationGatewayFirewallPolicyManagedRuleSet -RuleSetType $ruleSetType `
--RuleSetVersion $ruleSetVersion -RuleGroupOverrides $ruleGroupOverride1, $ruleGroupOverride2
+-RuleSetVersion $ruleSetVersion -RuleGroupOverride $ruleGroupOverride1, $ruleGroupOverride2
 ```
 
 Creates a ManagedRuleSet with ruleSetType as $ruleSetType, ruleSetVersion as $ruleSetVersion and RuleGroupOverrides as a list with entires as $ruleGroupOverride1, $ruleGroupOverride2