fix(suspensions): fix missing datetime cast

A missing datetime cast caused issues in the suspension service, where it tried calling Carbon methods on a string (which should have been a Carbon instance).

app/Ban.php

@@ -36,7 +36,7 @@ class Ban extends Model
     ];
 
     public $casts = [
-        'bannedUntil',
+        'bannedUntil' => 'datetime',
     ];
 
     public function user()