cli-p3: add -> None

Signed-off-by: Roman Volosatovs <rvolosatovs@riseup.net>

Author: rvolosatovs

examples/cli-p3/app.py

@@ -1,5 +1,5 @@
 from wit_world import exports
 
 class Run(exports.Run):
-    async def run(self):
+    async def run(self) -> None:
         print("Hello, world!")