test: mark never-called ASGI receive stubs as no cover

The 405 rejection paths return before the request body is read, so the
stub receive callables never execute. Matches the existing convention
for unreachable test helpers in this suite.

Author: Veerendra Kumar

tests/server/test_streamable_http_manager.py

@@ -772,7 +772,7 @@ async def mock_send(message: Message) -> None:
         }
 
         async def mock_receive() -> Message:
-            return {"type": "http.request", "body": b"", "more_body": False}
+            return {"type": "http.request", "body": b"", "more_body": False}  # pragma: no cover
 
         await manager.handle_request(scope, mock_receive, mock_send)
 

tests/shared/test_streamable_http.py

@@ -2290,7 +2290,7 @@ async def asgi_send(message: Message) -> None:
         sent.append(message)
 
     async def asgi_receive() -> Message:
-        return {"type": "http.request", "body": b"", "more_body": False}
+        return {"type": "http.request", "body": b"", "more_body": False}  # pragma: no cover
 
     # Send a GET request without a session ID header
     scope: Scope = {
@@ -2342,7 +2342,7 @@ async def asgi_send(message: Message) -> None:
         sent.append(message)
 
     async def asgi_receive() -> Message:
-        return {"type": "http.request", "body": b"", "more_body": False}
+        return {"type": "http.request", "body": b"", "more_body": False}  # pragma: no cover
 
     # Send a GET request with a WRONG session ID header
     scope: Scope = {