Update solipsism (#12)

Update solipsism to latest version and use modern way to replace event
loop

Author: Marenz

pyproject.toml

@@ -88,7 +88,7 @@ dev-pytest = [
   "frequenz-repo-config[extra-lint-examples] == 0.9.1",
   "pytest-mock == 3.12.0",
   "pytest-asyncio == 0.23.5",
-  "async-solipsism == 0.5",
+  "async-solipsism == 0.6",
   "time-machine == 2.14.0",
 ]
 dev = [

tests/test_frequenz_dispatch.py

@@ -24,12 +24,10 @@
 
 
 # This method replaces the event loop for all tests in the file.
-@fixture(scope="module")
-def event_loop() -> Iterator[async_solipsism.EventLoop]:
-    """Replace the loop with one that doesn't interact with the outside world."""
-    loop = async_solipsism.EventLoop()
-    yield loop
-    loop.close()
+@fixture
+def event_loop_policy() -> async_solipsism.EventLoopPolicy:
+    """Return an event loop policy that uses the async solipsism event loop."""
+    return async_solipsism.EventLoopPolicy()
 
 
 @fixture