Amend voltage documentation

Signed-off-by: daniel-zullo-frequenz <[email protected]>

Author: daniel-zullo-frequenz

src/frequenz/sdk/microgrid/_data_pipeline.py

@@ -140,7 +140,7 @@ def voltage(self) -> VoltageStreamer:
         """Fetch the 3-phase voltage for the microgrid.
 
         Returns:
-            The VoltageStreaming instance.
+            The VoltageStreamer instance.
         """
         if not self._voltage_instance:
             self._voltage_instance = VoltageStreamer(