Fix overzealous inference of "type" in subscript contexts

Ref pylint-dev/pylint#4083. Ref pylint-dev/pylint#4387. When used in a
nodes.Subscript, an existing inference_tip was set for Name nodes
matching called type. However, when this name was redefined this led to
false-positive typecheck errors in pylint such as invalid-sequence-index
(see pylint-dev/pylint#4083 and pylint-dev/pylint#4387)

Author: nelfin

astroid/brain/brain_type.py

@@ -17,7 +17,7 @@
 """
 import sys
 
-from astroid import MANAGER, extract_node, inference_tip, nodes
+from astroid import MANAGER, extract_node, inference_tip, nodes, UseInferenceDefault
 
 PY39 = sys.version_info >= (3, 9)
 
@@ -47,6 +47,8 @@ def infer_type_sub(node, context=None):
     :return: the inferred node
     :rtype: nodes.NodeNG
     """
+    if "type" in node.scope().locals:
+        raise UseInferenceDefault()
     class_src = """
     class type:
         def __class_getitem__(cls, key):

tests/unittest_inference.py

@@ -4012,6 +4012,19 @@ def func(type):
         assert not isinstance(inferred, nodes.ClassDef)  # was inferred as builtins.type
         assert inferred is util.Uninferable
 
+    @pytest.mark.skipif(sys.version_info < (3, 8), reason="only fails on Python 3.9")
+    def test_infer_arg_called_type_when_used_as_subscript_is_uninferable(self):
+        # Only this case seems to fail
+        node = extract_node(
+            """
+        def func(type):
+            type[0] #@
+        """
+        )
+        inferred = next(node.infer())
+        assert not isinstance(inferred, nodes.ClassDef)  # was inferred as builtins.type
+        assert inferred is util.Uninferable
+
 
 class GetattrTest(unittest.TestCase):
     def test_yes_when_unknown(self):