Dict union operator in Python 3.9 causes test failure

### Steps to reproduce

The below line where | is used for dictionaries is valid now with https://www.python.org/dev/peps/pep-0584/ in Python 3.9

 https://github.com/PyCQA/astroid/blob/25384d4bebf0187b6704c818c7df64945793362c/tests/unittest_inference.py#L2458

### Current behavior

Error is raised in Python 3.9

### Expected behavior

No error should be raised.

