Fix feature switch example (#11376)

Author: sbomer

xml/System.Diagnostics.CodeAnalysis/FeatureSwitchDefinitionAttribute.xml

@@ -61,10 +61,9 @@ When the app is trimmed with the following feature settings in the project file,
 
 ```xml
 <ItemGroup>
-  <RuntimeHostConfigurationOption Include="Feature.IsSupported" Value="false" />
+  <RuntimeHostConfigurationOption Include="Feature.IsSupported" Value="false" Trim="true" />
 </ItemGroup>
 ```
-
 ]]></format>
     </example>
   </Docs>