mail/snappymail: Fix error while accessing admin page

On a fresh installation, the admin page returns a 500 error, indicating
a web server error. The logs reveal what the problem is, which is already
fixed in upstream [1], but until a new version of snappymail is released,
the user will see the following error:

RainLoop\Config\Application::SetPassword(): Argument #1 ($oPassword) must be of type SnappyMail\SensitiveString, string given, called in /usr/local/www/snappymail/snapp
ymail/v/2.35.2/app/libraries/RainLoop/Actions.php on line 672

Reference: https://github.com/the-djmaze/snappymail/issues/1472 [1]
PR: 277571
MFH: 2024Q1
(cherry picked from commit 396010cb585aaaf9e3f87038f06760dece7e1fd7)