editor: tests: Fix object lifetime issue detected with PyQt6

Some tests explicitly close the editorstack widget. qtbot also closes
the widget after the test finishes. The latter action may fail when
"delete on close" flag is set => reset the flag.

spyder/plugins/editor/widgets/editorstack/tests/test_editorstack_and_outline.py

@@ -16,6 +16,7 @@
 
 # Third party imports
 import pytest
+from qtpy.QtCore import Qt
 
 # Local imports
 from spyder.config.base import running_in_ci
@@ -75,6 +76,11 @@ def _create_editorstack(files):
         editorstack.save_dialog_on_tests = True
         editorstack.set_outlineexplorer(outlineexplorer)
 
+        # Some tests explicitly close the editorstack widget. qtbot also
+        # closes the widget after the test finishes. The latter action
+        # may fail when "delete on close" flag is set => clear the flag.
+        editorstack.setAttribute(Qt.WA_DeleteOnClose, False)
+
         qtbot.addWidget(editorstack)
         editorstack.show()