uncomment migration tests (#40230)

mysql seems to have stopped flaking on them

test/metabase/db/schema_migrations_test.clj

@@ -264,8 +264,7 @@
           pg-field-3-id :type/Text
           mysql-field-1-id :type/JSON
           mysql-field-2-id :type/Text)
-        ;; TODO: this is commented out temporarily because it flakes for MySQL
-        #_(testing "Rollback restores the original state"
+        (testing "Rollback restores the original state"
            (migrate! :down 46)
            (let [new-base-types (t2/select-pk->fn :base_type Field)]
              (are [field-id expected] (= expected (get new-base-types field-id))
@@ -523,7 +522,6 @@
           (testing (str "View " view-name " should be created")
             ;; Just assert that something was returned by the query and no exception was thrown
             (is (partial= [] (t2/query (str "SELECT 1 FROM " view-name))))))
-        #_#_ ;; TODO: this is commented out temporarily because it flakes for MySQL (metabase#37434)
         (migrate! :down 47)
         (testing "Views should be removed when downgrading"
           (doseq [view-name new-view-names]