Code cleanup

app/Handlers/Observer/RecurrenceTransactionObserver.php

@@ -1,4 +1,5 @@
 <?php
+
 /*
  * RecurrenceTransactionObserver.php
  * Copyright (c) 2023 james@firefly-iii.org
@@ -18,6 +19,7 @@
  * You should have received a copy of the GNU Affero General Public License
  * along with this program.  If not, see <https://www.gnu.org/licenses/>.
  */
+declare(strict_types=1);
 
 namespace FireflyIII\Handlers\Observer;