Added missing comma (Azure#18585)

Added missing comma to the **Get a configuration setting** sample

Author: cmendible

sdk/data/azappconfig/README.md

@@ -142,7 +142,7 @@ func ExampleGetConfigurationSetting() {
     // Get configuration setting
     resp, err := client.GetSetting(
         context.TODO(),
-        "key"
+        "key",
         &azappconfig.GetSettingOptions{
             Label: to.Ptr("label")
         })