Fix test_replica_query_race flakiness (#8038)

This failed once with `relation "test" does not exist` when trying to
run the query on the standby. It's possible that the standby is started
before the CREATE TABLE is processed in the pageserver, and the standby
opens up for queries before it has received the CREATE TABLE transaction
from the primary. To fix, wait for the standby to catch up to the
primary before starting to run the queries.


https://neon-github-public-dev.s3.amazonaws.com/reports/pr-8025/9483658488/index.html

test_runner/regress/test_hot_standby.py

@@ -300,7 +300,7 @@ def test_replica_query_race(neon_simple_env: NeonEnv):
             p_cur.execute("CREATE TABLE test AS SELECT 0 AS counter")
 
     standby_ep = env.endpoints.new_replica_start(origin=primary_ep, endpoint_id="standby")
-    time.sleep(1)
+    wait_replica_caughtup(primary_ep, standby_ep)
 
     # In primary, run a lot of UPDATEs on a single page
     finished = False