fix: makes response writer error a debug message. (#1549)

* Makes response writer error a debug message.

* trigger

* log at warn level

* Update frankenphp.go

---------

Co-authored-by: Alliballibaba <alliballibaba@gmail.com>
Co-authored-by: Kévin Dunglas <kevin@dunglas.fr>

Author: AlliBalliBaba

frankenphp.go

@@ -533,7 +533,7 @@ func go_sapi_flush(threadIndex C.uintptr_t) bool {
 	}
 
 	if err := http.NewResponseController(fc.responseWriter).Flush(); err != nil {
-		logger.LogAttrs(context.Background(), slog.LevelError, "the current responseWriter is not a flusher", slog.Any("error", err))
+		logger.LogAttrs(context.Background(), slog.LevelWarn, "the current responseWriter is not a flusher, if you are not using a custom build, please report this issue", slog.Any("error", err))
 	}
 
 	return false