Fix #9752: autodoc: Failed to detect type annotation for slots attribute

tests/roots/test-ext-autodoc/target/slots.py

@@ -10,6 +10,7 @@ class Bar:
     __slots__ = {'attr1': 'docstring of attr1',
                  'attr2': 'docstring of attr2',
                  'attr3': None}
+    __annotations__ = {'attr1': int}
 
     def __init__(self):
         self.attr2 = None  #: docstring of instance attr2

tests/test_ext_autodoc.py

@@ -1359,6 +1359,7 @@ def test_slots(app):
         '',
         '   .. py:attribute:: Bar.attr1',
         '      :module: target.slots',
+        '      :type: int',
         '',
         '      docstring of attr1',
         '',

tests/test_ext_autodoc_autoattribute.py

@@ -129,6 +129,7 @@ def test_autoattribute_slots_variable_dict(app):
         '',
         '.. py:attribute:: Bar.attr1',
         '   :module: target.slots',
+        '   :type: int',
         '',
         '   docstring of attr1',
         '',

tests/test_ext_autodoc_autoclass.py

@@ -243,6 +243,7 @@ def test_slots_attribute(app):
         '',
         '   .. py:attribute:: Bar.attr1',
         '      :module: target.slots',
+        '      :type: int',
         '',
         '      docstring of attr1',
         '',