Increase timeout for wating subscriber caught-up (#8118)

## Problem

test_subscriber_restart has quit large failure rate'

https://neonprod.grafana.net/d/fddp4rvg7k2dcf/regression-test-failures?orgId=1&var-test_name=test_subscriber_restart&var-max_count=100&var-restrict=false

I can be caused by too small timeout (5 seconds) to wait until changes
are propagated.

Related to #8097

## Summary of changes

Increase timeout to 30 seconds.

## Checklist before requesting a review

- [ ] I have performed a self-review of my code.
- [ ] If it is a core feature, I have added thorough tests.
- [ ] Do we need to implement analytics? if so did you add the relevant
metrics to the dashboard?
- [ ] If this PR requires public announcement, mark it with
/release-notes label and add several sentences in this section.

## Checklist before merging

- [ ] Do not forget to reformat commit message to not include the above
checklist

Co-authored-by: Konstantin Knizhnik <[email protected]>

test_runner/regress/test_subscriber_restart.py

@@ -54,4 +54,4 @@ def insert_data(pub):
         pcur.execute(f"INSERT into t values ({n_records}, 0)")
         n_records += 1
         with sub.cursor() as scur:
-            wait_until(10, 0.5, check_that_changes_propagated)
+            wait_until(60, 0.5, check_that_changes_propagated)