[Bug]: The UI shows logs multiple times

[r4victor]

Steps to reproduce

1. Submit a run that prints one or more lines of logs:

type: task
nodes: 1
commands:
  - echo "12345"
  - echo "6789"

2. See the logs displayed many times in the UI:

Actual behaviour

The problem seems to be on the UI side (after #2915) since the UI makes many /logs/poll even if next_token is null.

Expected behaviour

No response

dstack version

master

Server logs

Additional information

No response