Fix HTTPException swallowed as 500 in /vantage/export endpoint

Add missing `except HTTPException: raise` guard so intentional 404
responses (e.g. when settings are not configured) are not caught by the
generic Exception handler and re-raised as 500 errors.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

litellm/proxy/spend_tracking/vantage_endpoints.py

@@ -487,6 +487,8 @@ async def vantage_export(
             summary=None,
         )
 
+    except HTTPException:
+        raise
     except Exception as e:
         verbose_proxy_logger.error(f"Error performing Vantage export: {str(e)}")
         raise HTTPException(