Replace #[allow attributes with expect (#7796)

We do have `clippy::allow_attributes` turned on, but it doesn't seem to
work properly

crates/epaint/src/stroke.rs

@@ -1,5 +1,3 @@
-#![allow(clippy::derived_hash_with_manual_eq)] // We need to impl Hash for f32, but we don't implement Eq, which is fine
-
 use std::{fmt::Debug, sync::Arc};
 
 use emath::GuiRounding as _;