fix: show slot_millis_sum warning only when allow_large_results=False (#1892)

Author: shobsi

bigframes/session/__init__.py

@@ -339,13 +339,15 @@ def bytes_processed_sum(self):
     @property
     def slot_millis_sum(self):
         """The sum of all slot time used by bigquery jobs in this session."""
-        msg = bfe.format_message(
-            "Queries executed with `allow_large_results=False` within the session will not "
-            "have their slot milliseconds counted in this sum.  If you need precise slot "
-            "milliseconds information, query the `INFORMATION_SCHEMA` tables "
-            "to get relevant metrics.",
-        )
-        warnings.warn(msg, UserWarning)
+        if not bigframes.options._allow_large_results:
+            msg = bfe.format_message(
+                "Queries executed with `allow_large_results=False` within the session will not "
+                "have their slot milliseconds counted in this sum.  If you need precise slot "
+                "milliseconds information, query the `INFORMATION_SCHEMA` tables "
+                "to get relevant metrics.",
+            )
+            warnings.warn(msg, UserWarning)
+
         return self._metrics.slot_millis
 
     @property