fix: use lax no cover for GET stream exception handler

This handler may be triggered in some CI configurations, so use lax
to avoid strict-no-cover failures while still excluding from coverage.

Author: maxisbey

src/mcp/client/streamable_http.py

@@ -200,7 +200,7 @@ async def handle_get_stream(self, client: httpx.AsyncClient, read_stream_writer:
                     # Stream ended normally (server closed) - reset attempt counter
                     attempt = 0
 
-            except Exception as exc:  # pragma: no cover
+            except Exception as exc:  # pragma: lax no cover
                 logger.debug(f"GET stream error: {exc}")
                 attempt += 1