fix use of deprecated rand API

src/tools/miri/src/operator.rs

@@ -120,6 +120,6 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
         let this = self.eval_context_ref();
         // Return one side non-deterministically.
         let mut rand = this.machine.rng.borrow_mut();
-        if rand.gen() { a } else { b }
+        if rand.random() { a } else { b }
     }
 }