TYP: add type annotation to `_xlwt.py` #36024
- [x] closes #36024
- [x] passes `black pandas`
- [x] passes `git diff upstream/master -u -- "*.py" | flake8 --diff`

pandas\io\excel\_xlwt.py:52: error: Need type annotation for 'style_dict' (hint: "style_dict: Dict[<type>, <type>] = ...")  [var-annotated]

Thanks @VirosaLi 