[12.x] Fix type casting for environment variables in config files (#6637)

* Update app.php

* Update cache.php

* Update database.php

* Update logging.php

* Update mail.php

config/mail.php

@@ -46,7 +46,7 @@ return [
             'username' => env('MAIL_USERNAME'),
             'password' => env('MAIL_PASSWORD'),
             'timeout' => null,
-            'local_domain' => env('MAIL_EHLO_DOMAIN', parse_url(env('APP_URL', 'http://localhost'), PHP_URL_HOST)),
+            'local_domain' => env('MAIL_EHLO_DOMAIN', parse_url((string) env('APP_URL', 'http://localhost'), PHP_URL_HOST)),
         ],
 
         'ses' => [