chore: suggest wrapping in an assert!() instead

This shortens the `#[must_use]` diagnostics displayed, in light of the [review comment](https://github.com/rust-lang/rust/pull/62431/files#r300819839) on when this was originally added.

library/core/src/option.rs

@@ -642,7 +642,7 @@ impl<T> Option<T> {
     /// assert_eq!(x.is_none(), true);
     /// ```
     #[must_use = "if you intended to assert that this doesn't have a value, consider \
-                  `.and_then(|_| panic!(\"`Option` had a value when expected `None`\"))` instead"]
+                  wrapping this in an `assert!()` instead"]
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
     #[rustc_const_stable(feature = "const_option_basics", since = "1.48.0")]