pickle.py raises wrong exceptions for Invalid Data

[djoume]

Steps to reproduce:

import pickle

invalid_data = b"this is not valid pickle data"
try:
    pickle.loads(invalid_data)
    assert False, "Expected UnpicklingError to be raised"
except pickle.UnpicklingError:
    assert True
except IndexError:
    print("IndexError raised instead of UnpicklingError")

from unittest.mock import patch, mock_open

with patch("builtins.open", mock_open(read_data=invalid_data)):
  with open("dummy_file", "rb") as f:
    try:
      pickle.load(f)
      assert False, "Expected UnpicklingError to be raised"
    except pickle.UnpicklingError:
      assert True
    except IndexError:
        print("IndexError raised instead of UnpicklingError")

Expected (CPython behaviour): no output

Actual:

IndexError raised instead of UnpicklingError
IndexError raised instead of UnpicklingError

Note this is actually a bug in CPython's standard library: python/cpython#141749