fix: ignore verification error if the chat is not protected yet

[link2xt]

If we receive a message from non-verified contact
in a non-protected chat with a Chat-Verified header, there is no need to upgrade the chat
to verified and display an error.

If it was an attack, an attacker could
just not send the Chat-Verified header.
Most of the time, however, it is just
message reordering.

Closes #6408

[Hocuri]

The change LGTM, but shouldn't we additionally change this code:

    let create_protected = if mime_parser.get_header(HeaderDef::ChatVerified).is_some() {
        if let VerifiedEncryption::NotVerified(err) = verified_encryption {
            warn!(context, "Verification problem: {err:#}.");
            let s = format!("{err}. See 'Info' for more details");
            mime_parser.replace_msg_by_error(&s);
        }
        ProtectionStatus::Protected
    } else {
        ProtectionStatus::Unprotected
    };

in create_group()?

Because right now, probably the following still results in the bug (even though I didn't test):

• Bob and Charlie are already verified
• Bob and Alice are already verified
• Bob and Alice create a verified group
• Bob manually adds Charlie to the verified group, but Charlie doesn't receive the message yet
• Alice sends a .xdc to Charlie

[link2xt]

but shouldn't we additionally change this code

I changed the code and extended existing test.

[Hocuri]

Nice and simple solution for this problem!

[link2xt]

There is a Python test broken with a second commit, need to adjust it, will merge then.