Fix type error in lint description (#14466)

Fix #14465

changelog: none

Author: blyxyas

Diff for: clippy_lints/src/casts/mod.rs

@@ -71,7 +71,7 @@ declare_clippy_lint! {
     /// ### Example
     /// ```no_run
     /// let y: i8 = -1;
-    /// y as u128; // will return 18446744073709551615
+    /// y as u64; // will return 18446744073709551615
     /// ```
     #[clippy::version = "pre 1.29.0"]
     pub CAST_SIGN_LOSS,