The `vector_store_client_test_dns_resolving_repeated` test had race
conditions causing it to be flaky. Two main issues were identified:
1. Race between initial refresh and manual trigger: The test assumes
a specific resolution sequence, but timing variations between the
initial DNS refresh (on client creation) and the first manual
trigger (in the test loop) can cause unexpected delayed scheduling.
2. Extra triggers from resolve_hostname fiber: During the client
refresh phase, the background DNS fiber clears the client list.
If resolve_hostname executes in the window after clearing but
before the update completes, pending triggers are processed,
incrementing the resolution count unexpectedly. At count 6, the
mock resolver returns a valid address (count % 3 == 0), causing
the test to fail.
The fix relaxes test assertions to verify retry behavior and client
clearing on DNS address loss, rather than enforcing exact resolution
counts.
Fixes: #27074Closesscylladb/scylladb#27685
addac8b3f7