fix: add pragma for ClientDisconnect handler unreachable via ASGITransport

ClientDisconnect only occurs with real TCP connections; ASGITransport
used in tests cannot trigger it.

Github-Issue:#1648

Author: skyvanguard

src/mcp/server/streamable_http.py

@@ -388,7 +388,7 @@ async def handle_request(self, scope: Scope, receive: Receive, send: Send) -> No
                 await self._handle_delete_request(request, send)
             else:  # pragma: no cover
                 await self._handle_unsupported_request(request, send)
-        except ClientDisconnect:
+        except ClientDisconnect:  # pragma: no cover
             logger.debug(f"Client disconnected during {request.method} request")
 
     def _check_accept_headers(self, request: Request) -> tuple[bool, bool]: