MAINT: Allow another clippy lint

This one complains about if let Some(_) = option; which I still think is
just as fine as if option.is_some(); `if let` is a nice Rust feature
that works the same way on all enums, no reason to prefer
option-specific methods like `is_some`.

src/lib.rs

@@ -10,6 +10,7 @@
 #![doc(html_logo_url = "https://rust-ndarray.github.io/images/rust-ndarray_logo.svg")]
 #![allow(
     unstable_name_collisions, // our `PointerExt` collides with upcoming inherent methods on `NonNull`
+    clippy::redundant_pattern_matching, // if let is sometimes good style
     clippy::many_single_char_names,
     clippy::deref_addrof,
     clippy::unreadable_literal,