Fix unexpected bugs in v3

Author: leandrodamascena

examples/event_handler_rest/src/accessing_request_details_headers.py

@@ -16,7 +16,7 @@
 def get_todos():
     endpoint = "https://jsonplaceholder.typicode.com/todos"
 
-    api_key = app.current_event.headers["X-Api-Key"]
+    api_key = app.current_event.headers.get("X-Api-Key")
     todos: Response = requests.get(endpoint, headers={"X-Api-Key": api_key})
     todos.raise_for_status()