Updating unused variable in tests to _

Author: annahay4

rust-runtime/aws-smithy-runtime/src/client/retries/token_bucket.rs

@@ -523,7 +523,7 @@ mod tests {
         let iterations = 5;
 
         // Accumulate fractional tokens
-        for i in 1..=iterations {
+        for _ in 1..=iterations {
             let current = atomic.load();
             atomic.store(current + success_reward);
         }