KeyError in _set_proxied with getset_descriptor class

[correctmost]

Steps to reproduce

The following code triggers a KeyError in astroid:

dict.fromkeys.__doc__.c=p

This bug was discovered by OSS-Fuzz:
https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=62324 (report not public yet)

Current behavior

Traceback (most recent call last):
  File "pylint/pylint/utils/ast_walker.py", line 91, in walk
    callback(astroid)
  File "pylint/pylint/checkers/classes/class_checker.py", line 1739, in visit_assignattr
    self._check_in_slots(node)
  File "pylint/pylint/checkers/classes/class_checker.py", line 1774, in _check_in_slots
    inferred = safe_infer(node.expr)
               ^^^^^^^^^^^^^^^^^^^^^
  File "pylint/pylint/checkers/utils.py", line 1372, in safe_infer
    inferred_types.add(_get_python_type_of_node(value))
                       ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "pylint/pylint/checkers/utils.py", line 1339, in _get_python_type_of_node
    return pytype()
           ^^^^^^^^
  File "astroid/astroid/nodes/node_classes.py", line 2159, in pytype
    return self._proxied.qname()
           ^^^^^^^^^^^^^
  File "astroid/astroid/raw_building.py", line 596, in _set_proxied
    return _CONST_PROXY[const.value.__class__]
           ~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^^^^^^
KeyError: <class 'getset_descriptor'>

Expected behavior

No crash

Version

d8dbc46

[correctmost]

The crash was fixed by 523eeb4.