Update binary_sensor.template.markdown (#10007)

The example was corrected, but is now wrong, so I have made it wrong again, which is now correct

source/_components/binary_sensor.template.markdown

@@ -85,7 +85,7 @@ Template Binary Sensor may get an `unknown` state during startup. This results
 in error messages in your log file until that platform has completed loading.
 If you use `is_state()` function in your template, you can avoid this situation.
 For example, you would replace
-{% raw %}`{{ is_state('switch.source', 'on') }}`{% endraw %}
+{% raw %}`{{ states.switch.source.state == 'on' }}`{% endraw %}
 with this equivalent that returns `true`/`false` and never gives an unknown
 result:
 {% raw %}`{{ is_state('switch.source', 'on') }}`{% endraw %}