Update postcode in tests as the old one stopped working for some reason

tests/Service/GeocoderTest.php

@@ -18,8 +18,8 @@ use Symfony\Bundle\FrameworkBundle\Test\KernelTestCase;
  */
 final class GeocoderTest extends KernelTestCase
 {
-    // Buckingham Palace
-    private const string POSTCODE = 'SW1A 1AA';
+    // Yes this is a real postcode
+    private const string POSTCODE = 'ABC 123';
 
     private Geocoder $geocoder;