qt brain: Make slot argument optional for disconnect()

ChangeLog

@@ -23,6 +23,8 @@ What's New in astroid 2.11.6?
 =============================
 Release date: TBA
 
+* The Qt brain now correctly treats calling ``.disconnect()`` (with no
+  arguments) on a slot as valid.
 
 What's New in astroid 2.11.5?
 =============================

astroid/brain/brain_qt.py

@@ -24,10 +24,12 @@ def _looks_like_signal(node, signal_name="pyqtSignal"):
 def transform_pyqt_signal(node: nodes.FunctionDef) -> None:
     module = parse(
         """
+    _UNSET = object()
+
     class pyqtSignal(object):
         def connect(self, slot, type=None, no_receiver_check=False):
             pass
-        def disconnect(self, slot):
+        def disconnect(self, slot=_UNSET):
             pass
         def emit(self, *args):
             pass

tests/unittest_brain_qt.py

@@ -52,3 +52,21 @@ def test_implicit_parameters() -> None:
             pytest.skip("PyQt6 C bindings may not be installed?")
         assert isinstance(attribute_node, FunctionDef)
         assert attribute_node.implicit_parameters() == 1
+
+    @staticmethod
+    def test_slot_disconnect_no_args() -> None:
+        """Test calling .disconnect() on a signal.
+
+        See https://github.com/PyCQA/astroid/pull/1531#issuecomment-1111963792
+        """
+        src = """
+        from PyQt6.QtCore import QTimer
+        timer = QTimer()
+        timer.timeout.disconnect  #@
+        """
+        node = extract_node(src)
+        attribute_node = node.inferred()[0]
+        if attribute_node is Uninferable:
+            pytest.skip("PyQt6 C bindings may not be installed?")
+        assert isinstance(attribute_node, FunctionDef)
+        assert attribute_node.args.defaults