[tests] Fix expected failure type random selector (#20652)

## Description 

The change of this code block from `Ok(rand::random())` to a custom
selector logic overlooked the fact that we must avoid re-selecting
variant `0`, as variant `0` is the random variant, causing the code to
hit an `unreachable` block meant to avoid infinte recursion.

## Test plan 

Re-run test

---

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crates/sui-benchmark/src/workloads/workload.rs

@@ -47,7 +47,7 @@ impl TryFrom<u32> for ExpectedFailureType {
         match value {
             0 => {
                 let mut rng = rand::thread_rng();
-                let n = rng.gen_range(0..ExpectedFailureType::COUNT - 1);
+                let n = rng.gen_range(1..ExpectedFailureType::COUNT - 1);
                 Ok(ExpectedFailureType::iter().nth(n).unwrap())
             }
             _ => ExpectedFailureType::iter()