bug#68962: website: directly link the security mail address

[Jonathan Brielmaier]

Is there a reason why we don't link to the mail alias directly on the
security page:
https://guix.gnu.org/en/security/

Because the mailman archive doesn't make really sense for most of the
users as it's only accessible with a password.

What about this small patch?
```
diff --git a/website/apps/base/templates/security.scm
b/website/apps/base/templates/security.scm
index 8a72950..429e5df 100644
--- a/website/apps/base/templates/security.scm
+++ b/website/apps/base/templates/security.scm
@@ -43,7 +43,7 @@ system|GNU Hurd|GNU Guix package manager|Security
updates") #\|)
         `(p
           "To report sensitive security issues in Guix itself or the
            packages it provides, you can write to the private mailing
list "
-          (a (@ (href
"https://lists.gnu.org/mailman/listinfo/guix-security";))
+          (a (@ (href "mailto:guix-security@gnu.org";))
              ("guix-security@gnu.org")) ".  This list is monitored by a
            small team of Guix developers."))
       ,(G_
```

Or is this an anti-spam measure?

~Jonathan