use the errmsg as the status description instead of the _DocumentOut

Author: toshok

instrumentation/opentelemetry-instrumentation-pymongo/src/opentelemetry/instrumentation/pymongo/__init__.py

@@ -198,7 +198,7 @@ def failed(self, event: monitoring.CommandFailedEvent):
         if span is None:
             return
         if span.is_recording():
-            span.set_status(Status(StatusCode.ERROR, event.failure))
+            span.set_status(Status(StatusCode.ERROR, event.failure.get("errmsg", "Unknown error")))
             try:
                 self.failed_hook(span, event)
             except (