Fix clickbench avg time compute (#15472)

Author: zhuqi-lucas

benchmarks/src/clickbench.rs

@@ -129,9 +129,9 @@ impl RunOpt {
         self.register_hits(&ctx).await?;
 
         let iterations = self.common.iterations;
-        let mut millis = Vec::with_capacity(iterations);
         let mut benchmark_run = BenchmarkRun::new();
         for query_id in query_range {
+            let mut millis = Vec::with_capacity(iterations);
             benchmark_run.start_new_case(&format!("Query {query_id}"));
             let sql = queries.get_query(query_id)?;
             println!("Q{query_id}: {sql}");