[9.20] fix: test: Increase timeout for reload-based kasp signing checks

[9.20] fix: test: Increase timeout for reload-based kasp signing checks

```
______________________________ test_kasp_default _______________________________
[gw0] freebsd15 -- Python 3.11.15 /usr/local/bin/python3.11
/home/ec2-user/builds/isc-private/bind9/bin/tests/system/kasp/tests_kasp.py:910: in test_kasp_default
    isctest.run.retry_with_timeout(update_is_signed, timeout=5)
/home/ec2-user/builds/isc-private/bind9/bin/tests/system/isctest/run.py:164: in retry_with_timeout
    assert False, msg
E   AssertionError: tests_kasp.test_kasp_default.<locals>.update_is_signed() timed out after 5 s
E   assert False
```

Backport of MR !12151

Merge branch 'backport-mnowak/kasp-default-update-is-signed-timeout-9.20' into 'bind-9.20'

See merge request isc-projects/bind9!12155