Increase query expvar timeout (#20630) (#20711)

(cherry picked from commit f2ee8dc)

Co-authored-by: Eric <22215921+ericywl@users.noreply.github.com>

Author: mergify[bot]

systemtest/benchtest/expvar/metrics.go

@@ -263,7 +263,7 @@ func run(ctx context.Context, serverURL string, period time.Duration) (<-chan ex
 				return
 			case <-ticker.C:
 				var e expvar
-				ctxWithTimeout, cancel := context.WithTimeout(ctx, period+5*time.Second)
+				ctxWithTimeout, cancel := context.WithTimeout(ctx, period+30*time.Second)
 				err := queryExpvar(ctxWithTimeout, &e, serverURL)
 				cancel()
 				if err != nil {