chore: adjust and cleanup tests

tests/Form/Service/ParticipantInsuranceFieldHandlerTest.php

@@ -250,7 +250,7 @@ class ParticipantInsuranceFieldHandlerTest extends TestCase
     private function createInsurance(string|int $id, string $label = 'Test Insurance'): Insurance
     {
         $insurance = new Insurance();
-        $insurance->id = $id;
+        $insurance->id = (string) $id;
         $insurance->label = $label;
 
         return $insurance;