Update sgp_tracing_processor.py

Author: smoreinis

src/agentex/lib/core/tracing/processors/sgp_tracing_processor.py

@@ -82,7 +82,7 @@ def __init__(self, config: SGPTracingProcessorConfig):
     def _add_source_to_span(self, span: Span) -> None:
         if span.data is None:
             span.data = {}
-        span.data["source"] = "agentex"
+        span.data["__source__"] = "agentex"
 
     @override
     async def on_span_start(self, span: Span) -> None: