mail/snappymail: Add missing ctype extension

When the user first logs in to its web server with snappymail installed, the first
thing it will see is:

[302] The following PHP extensions are not available in your PHP configuration!

    ctype

PR: 277570
MFH: 2024Q1
(cherry picked from commit 44b591df85b45b63a612c55de7cc1677fa9b484f)