fixup! Move container-specific method from base class

tests/gui/test_main_window.py

@@ -15,6 +15,7 @@
 from dangerzone.gui import main_window as main_window_module
 from dangerzone.gui import updater as updater_module
 from dangerzone.gui.logic import DangerzoneGui
+from dangerzone.isolation_provider.dummy import Dummy
 
 # import Pyside related objects from here to avoid duplicating import logic.
 from dangerzone.gui.main_window import (
@@ -510,9 +511,9 @@ def test_not_available_container_tech_exception(
 ) -> None:
     # Setup
     mock_app = mocker.MagicMock()
-    dummy = mocker.MagicMock()
-
-    dummy.is_runtime_available.side_effect = NotAvailableContainerTechException(
+    dummy = Dummy()
+    fn = mocker.patch.object(dummy, "is_runtime_available")
+    fn.side_effect = NotAvailableContainerTechException(
         "podman", "podman image ls logs"
     )