Fix the disable_actor_auto_restart fixture (#97)

The fixture didn't always work because in cases where the actor kept
running past the pytest session end, and failed then, the original
restart limit was reestablished, running into the infinite loop again.

Maybe related to #41.

Author: llucax

tests/conftest.py

@@ -15,13 +15,12 @@
 def disable_actor_auto_restart():  # type: ignore
     """Disable auto-restart of actors while running tests.
 
-    Since this is auto-use, the yield part (and restore of the variable) is not
-    strictly needed, but we leave it as an example.
+    At some point we had a version that would set the limit back to the
+    original value but it doesn't work because some actors will keep running
+    even after the end of the session and fail after the original value was
+    reestablished, getting into an infinite loop again.
 
     Note: Test class must derive after unittest.IsolatedAsyncioTestCase.
     Otherwise this fixture won't run.
     """
-    original_restart_limit = _decorator.BaseActor.restart_limit
     _decorator.BaseActor.restart_limit = 0
-    yield
-    _decorator.BaseActor.restart_limit = original_restart_limit