Fix instance_attrs building error in Qt brain

ChangeLog

@@ -12,6 +12,9 @@ What's New in astroid 2.11.3?
 =============================
 Release date: TBA
 
+* Fixed an error in the Qt brain when building ``instance_attrs``.
+
+  Closes PyCQA/pylint#6221
 
 
 What's New in astroid 2.11.2?

astroid/brain/brain_qt.py

@@ -34,9 +34,9 @@ def emit(self, *args):
     """
     )
     signal_cls = module["pyqtSignal"]
-    node.instance_attrs["emit"] = signal_cls["emit"]
-    node.instance_attrs["disconnect"] = signal_cls["disconnect"]
-    node.instance_attrs["connect"] = signal_cls["connect"]
+    node.instance_attrs["emit"] = [signal_cls["emit"]]
+    node.instance_attrs["disconnect"] = [signal_cls["disconnect"]]
+    node.instance_attrs["connect"] = [signal_cls["connect"]]
 
 
 def transform_pyside_signal(node):
@@ -52,9 +52,9 @@ def emit(self, *args):
     """
     )
     signal_cls = module["NotPySideSignal"]
-    node.instance_attrs["connect"] = signal_cls["connect"]
-    node.instance_attrs["disconnect"] = signal_cls["disconnect"]
-    node.instance_attrs["emit"] = signal_cls["emit"]
+    node.instance_attrs["connect"] = [signal_cls["connect"]]
+    node.instance_attrs["disconnect"] = [signal_cls["disconnect"]]
+    node.instance_attrs["emit"] = [signal_cls["emit"]]
 
 
 def pyqt4_qtcore_transform():

requirements_test_brain.txt

@@ -3,6 +3,7 @@ types-attrs
 nose
 numpy>=1.17.0
 python-dateutil
+PyQt6
 types-python-dateutil
 six
 types-six

tests/unittest_brain_qt.py

@@ -0,0 +1,36 @@
+# Licensed under the LGPL: https://www.gnu.org/licenses/old-licenses/lgpl-2.1.en.html
+# For details: https://github.com/PyCQA/astroid/blob/main/LICENSE
+# Copyright (c) https://github.com/PyCQA/astroid/blob/main/CONTRIBUTORS.txt
+
+from importlib.util import find_spec
+
+import pytest
+
+from astroid import extract_node
+from astroid.bases import UnboundMethod
+from astroid.manager import AstroidManager
+from astroid.nodes import FunctionDef
+
+HAS_PYQT6 = find_spec("PyQt6")
+
+
+@pytest.mark.skipif(HAS_PYQT6 is None, reason="This test requires the PyQt6 library.")
+class TestBrainQt:
+    @staticmethod
+    def test_value_of_lambda_instance_attrs_is_list():
+        """Regression test for https://github.com/PyCQA/pylint/issues/6221
+
+        A crash occurred in pylint when a nodes.FunctionDef was iterated directly,
+        giving items like "self" instead of iterating a one-element list containing
+        the wanted nodes.FunctionDef.
+        """
+        src = """
+        from PyQt6 import QtPrintSupport as printsupport
+        printsupport.QPrintPreviewDialog.paintRequested  #@
+        """
+        AstroidManager.brain["extension_package_whitelist"] = {"PyQt6.QtPrintSupport"}
+        node = extract_node(src)
+        attribute_node = node.inferred()[0]
+        # scoped_nodes.Lambda.instance_attrs is typed as Dict[str, List[NodeNG]]
+        assert isinstance(attribute_node, UnboundMethod)
+        assert isinstance(attribute_node.instance_attrs["connect"][0], FunctionDef)