fixing a typo (#14779)

'IncludeContext' parameter accepts boolean values and 'true' is a string. It should be '$true'

Author: PrateekKumarSingh

src/AlertsManagement/AlertsManagement/help/Get-AzAlert.md

@@ -42,7 +42,7 @@ Get-AzAlert [-TargetResourceId <String>] [-MonitorService <String>] [-MonitorCon
 
 ### Example 1
 ```powershell
-PS C:\> Get-AzAlert -Severity "Sev2" -MonitorCondition "Fired" -IncludeContext true
+PS C:\> Get-AzAlert -Severity "Sev2" -MonitorCondition "Fired" -IncludeContext $true
 ```
 
 List all alerts with Sev2 severity and Fired monitor condition. Setting IncludeContext to true, include custom payload of alert.