TYP: misc typing cleanup for core/computation/expressions.py
pandas\core\computation\expressions.py:78: error: Need type annotation for 'dtypes' (hint: "dtypes: Set[<type>] = ...")  [var-annotated]
pandas\core\computation\expressions.py:258: error: Need type annotation for '_TEST_RESULT' (hint: "_TEST_RESULT: List[<type>] = ...")  [var-annotated]
LGTM thanks @simonjayhawkins 