ruff

8dab7e4d - [ty] Improve diagnostics for subscriptions of non-generic types (#23516)

[ty] Improve diagnostics for subscriptions of non-generic types (#23516) ## Summary This PR contains some minor followups to https://github.com/astral-sh/ruff/pull/21840 to improve our diagnostics in a few places. I've had this patch hanging around locally for a while and can't remember exactly what I had thought there still was to do on it anymore... I think these are still worthwhile improvements, anyway! ## Test Plan Snapshots