Reduce the duration of the pgbench test.

We'll want to run it for longer when doing benchmarking, but 5 seconds
should be enough to tease out any basic bugs.

integration_tests/tests/test_pageserver.rs

@@ -80,7 +80,7 @@ fn pgbench() {
     let node = compute_cplane.new_test_node(maintli);
     node.start().unwrap();
 
-    let status = node.pg_bench(10, 100);
+    let status = node.pg_bench(10, 5);
     assert!(status.success());
 }