Account for removal of UB in float-to-int casts

This updates the reference per PR rust-lang/rust#71269.

Author: Mark-Simulacrum

src/expressions/operator-expr.md

@@ -366,9 +366,8 @@ same trait object.
         * zero-extend if the source is unsigned
         * sign-extend if the source is signed
     * Casting from a float to an integer will round the float towards zero
-        * **[NOTE: currently this will cause Undefined Behavior if the rounded
-          value cannot be represented by the target integer type][float-int]**.
-          This includes Inf and NaN. This is a bug and will be fixed.
+        * `NaN` will return `0` and values outside the integer range will
+          saturate to the integer minimum/maximum.
     * Casting from an integer to float will produce the closest possible float \*
         * if necessary, rounding is according to `roundTiesToEven` mode \*\*\*
         * on overflow, infinity (of the same sign as the input) is produced