website/docs: fix transports example (#9074)

Update transports.md

request.context['notification'].body is correct.

Signed-off-by: Mrs Feathers <echo@furryrefuge.com>

website/docs/events/transports.md

@@ -27,7 +27,7 @@ Starting in 2021.9, you can also select a Notification mapping. This allows you
 
 ```python
 return {
-    "foo": context['notification'].body,
+    "foo": request.context['notification'].body,
 }
 ```