[BE] Enable Ruff's Flake8 PYI042 (#111114)
Enable [snake-case-type-alias (PYI042)](https://docs.astral.sh/ruff/rules/snake-case-type-alias/)
Link: #110950
Pull Request resolved: https://github.com/pytorch/pytorch/pull/111114
Approved by: https://github.com/albanD
