S/MIME: Lock Menu: Green lock is shown when message is enc+sign but signature verification fails

[st3iny]

Steps to reproduce

1. Sign (opaque), encrypt and send an email.
2. Import the S/MIME certificate of the recipient.
3. Don't import the CA certificate of the recipients.
4. Open the mail.
5. Observe that the lock is green.

Expected behavior

There should be a warning that the signature verification failed.

Ref #7962

Actual behavior

The lock is green and no warning about the unverified signature is shown.

Mail app version

main