Improve wording for getting an async iterator

We are not really initializing anything here, just returning.

Signed-off-by: Leandro Lucarella <[email protected]>

Author: llucax

src/frequenz/channels/_receiver.py

@@ -191,7 +191,7 @@ def consume(self) -> _T_co:
         """
 
     def __aiter__(self) -> Self:
-        """Initialize the async iterator over received values.
+        """Get an async iterator over the received values.
 
         Returns:
             This receiver, as it is already an async iterator.