chore: remove stale no-cover pragma now hit by invalid-UTF-8 test

Author: maxisbey

src/mcp/server/stdio.py

@@ -58,7 +58,7 @@ async def stdin_reader():
                 async for line in stdin:
                     try:
                         message = types.jsonrpc_message_adapter.validate_json(line, by_name=False)
-                    except Exception as exc:  # pragma: no cover
+                    except Exception as exc:
                         await read_stream_writer.send(exc)
                         continue