Update library/core/src/time.rs

Co-authored-by: Celina G. Val <[email protected]>

Author: sgpthomas

library/core/src/time.rs

@@ -794,7 +794,7 @@ impl Duration {
                   without modifying the original"]
     #[inline]
     #[rustc_const_stable(feature = "duration_consts_2", since = "1.58.0")]
-    #[ensures(|duration| !duration.is_some() || duration.unwrap().is_safe())]
+    #[ensures(|duration| duration.is_none() || duration.unwrap().is_safe())]
     pub const fn checked_mul(self, rhs: u32) -> Option<Duration> {
         // Multiply nanoseconds as u64, because it cannot overflow that way.
         let total_nanos = self.nanos.0 as u64 * rhs as u64;