Fix unclosed event loop warning in test

Previously, we were unnecessarily setting the solipsism
event loop as the default one and resulted in a test
warning due to unclosed event loops.

Signed-off-by: Daniel Zullo <[email protected]>

Author: daniel-zullo-frequenz

tests/microgrid/test_datapipeline.py

@@ -23,7 +23,6 @@
 def event_loop() -> Iterator[async_solipsism.EventLoop]:
     """Replace the loop with one that doesn't interact with the outside world."""
     loop = async_solipsism.EventLoop()
-    asyncio.set_event_loop(loop)  # Set the loop as default
     yield loop
     loop.close()