Store references to streaming tasks (#615)

This makes sure they don't get garbage collected.

Author: shsms

RELEASE_NOTES.md

@@ -119,3 +119,5 @@ This release replaces the `@actor` decorator with a new `Actor` class.
 - Fix `consumer_power` and `producer_power` similar to `pv_power`
 
 - Zero value requests received by the `PowerDistributingActor` will now always be accepted, even when there are non-zero exclusion bounds.
+
+- Hold on to a reference to all streaming tasks in the microgrid API client, so they don't get garbage collected.

src/frequenz/sdk/microgrid/client/_client.py

@@ -216,6 +216,7 @@ def __init__(
         self.target = target
         self.api = MicrogridStub(grpc_channel)
         self._component_streams: Dict[int, Broadcast[Any]] = {}
+        self._streaming_tasks: Dict[int, asyncio.Task[None]] = {}
         self._retry_spec = retry_spec
 
     async def components(self) -> Iterable[Component]:
@@ -401,7 +402,7 @@ def _get_component_data_channel(
         chan = Broadcast[_GenericComponentData](task_name)
         self._component_streams[component_id] = chan
 
-        asyncio.create_task(
+        self._streaming_tasks[component_id] = asyncio.create_task(
             self._component_data_task(
                 component_id,
                 transform,