fix(test): fix a timing issue in pubsub test

[cxljs]

I found this bug in the CI: https://github.com/redis/go-redis/actions/runs/20411291539/job/58648503217?pr=3654

the log:

PubSub [It] should ChannelMessage
/home/runner/work/go-redis/go-redis/pubsub_test.go:562

  [FAILED] Timed out after 1.000s.
  Expected
      <<-chan *redis.Message | len:0, cap:10>: 0xc000a82ee0
  to receive something.
  In [It] at: /home/runner/work/go-redis/go-redis/pubsub_test.go:576 @ 12/21/25 14:35:54.367