Fix an H2 sync timezone test issue [ci drivers]

An incorrect query was written to pull the test-data DB that depending
on the order the tests were ran, would querying against a Druid DB
accidentally instead of the H2 db.

test/metabase/sync/sync_metadata/sync_timezone_test.clj

@@ -19,11 +19,15 @@
 (datasets/expect-with-engines #{:h2 :postgres}
   [{:timezone-id "UTC"} true true true]
   (data/dataset test-data
-    (let [db              (db/select-one Database [:name "test-data"])
+    (let [db              (data/db)
           tz-on-load      (db-timezone db)
           _               (db/update! Database (:id db) :timezone nil)
           tz-after-update (db-timezone db)]
 
+      ;; It looks like we can get some stale timezone information depending on which thread is used for querying the
+      ;; database in sync. Clearing the connection pool to ensure we get the most updated TZ data
+      (tu/clear-connection-pool db)
+
       [(sut/only-step-keys (sut/sync-database! "sync-timezone" db))
        ;; On startup is the timezone specified?
        (boolean (time/time-zone-for-id tz-on-load))
@@ -35,7 +39,7 @@
 (datasets/expect-with-engines #{:postgres}
   ["UTC" "UTC"]
   (data/dataset test-data
-    (let [db (db/select-one Database [:name "test-data"])]
+    (let [db (data/db)]
       (sync-tz/sync-timezone! db)
       [(db-timezone db)
        ;; This call fails as the dates on PostgreSQL return 'AEST'

test/metabase/test/util.clj

@@ -437,7 +437,7 @@
                                   {:cron-schedule (.getCronExpression ^CronTrigger trigger)
                                    :data          (into {} (.getJobDataMap trigger))}))))}))))))
 
-(defn- clear-connection-pool
+(defn clear-connection-pool
   "It's possible that a previous test ran and set the session's timezone to something, then returned the session to
   the pool. Sometimes that connection's session can remain intact and subsequent queries will continue in that
   timezone. That causes problems for tests that we can determine the database's timezone. This function will reset the