enable fallback interrupt randomization

fuzzers/FRET/src/systemstate/mutational.rs

@@ -375,7 +375,7 @@ where
                         }
                     }
                 }
-                #[cfg(not(feature = "trace_stg"))]
+                #[cfg(not(feature = "mutate_stg"))]
                 {
                     if myrand.between(1,100) <= 25 {  // we have no hint if interrupt times will change anything
                         do_rerun = true;