Include refused timestamp in exception message for easier debugging

Signed-off-by: Mathias L. Baumann <[email protected]>

Author: Marenz

src/frequenz/sdk/timeseries/_ringbuffer.py

@@ -130,7 +130,7 @@ def update(self, sample: Sample) -> None:
         # Don't add outdated entries
         if timestamp < self._datetime_oldest and self._datetime_oldest != datetime.max:
             raise IndexError(
-                f"Timestamp too old (cut-off is at {self._datetime_oldest})."
+                f"Timestamp {timestamp} too old (cut-off is at {self._datetime_oldest})."
             )
 
         # Update timestamps