[11.x] Remove incorrect syntax from mail's message template

Author: crynobone

src/Illuminate/Mail/resources/views/html/message.blade.php

@@ -13,7 +13,7 @@
 @isset($subcopy)
 <x-slot:subcopy>
 <x-mail::subcopy>
-{!! $subcopy !!}}
+{!! $subcopy !!}
 </x-mail::subcopy>
 </x-slot:subcopy>
 @endisset