chore: fix minor mypy type complaint in samples

Signed-off-by: Hal Blackburn <hwtb2@cam.ac.uk>

Author: h4l

samples/http-image-cloudevents/client.py

@@ -25,7 +25,7 @@
 image_bytes = resp.content
 
 
-def send_binary_cloud_event(url: str):
+def send_binary_cloud_event(url: str) -> None:
     # Create cloudevent
     attributes = {
         "type": "com.example.string",
@@ -42,7 +42,7 @@ def send_binary_cloud_event(url: str):
     print(f"Sent {event['id']} of type {event['type']}")
 
 
-def send_structured_cloud_event(url: str):
+def send_structured_cloud_event(url: str) -> None:
     # Create cloudevent
     attributes = {
         "type": "com.example.base64",