fix(test): add sleep to avoid race in stream route DNS test

The curl to port 9100 was firing before the etcd stream-route change
propagated to the stream workers, causing 'matched route: null' and
skipping DNS resolution. Add a 1s sleep after the admin PUT to let
the config sync complete before making the test request.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: nic-6443

t/cli/test_dns.sh

@@ -158,6 +158,7 @@ curl -v -k -i -m 20 -o /dev/null -s -X PUT http://127.0.0.1:9180/apisix/admin/st
         }
     }'
 
+sleep 1  # wait for the stream route to propagate from etcd to stream workers
 curl http://127.0.0.1:9100 || true
 make stop
 sleep 0.1 # wait for logs output