Include the Attachment header when the "an email should have been sent with" step does not match

[makmic]

I noticed that the debugging experience of the email matching step is not the best when you're asserting the Attachments header with an invalid value. For example:

      And an email should have been sent with:
        """
        From: [email protected]
        To: [email protected]
        Subject: My subject
        Attachments: logo.png

        Dear Mr Bar Foo,

If the actual e-mail has an attachment called icon.png instead of logo.png, spreewald currently outputs such a message:

No matching mail was found. There were 1 mails in total.
0 of those had matching headers.
Expected
--------------------------------------------------------------------------------
From: [email protected]
To: [email protected]
Subject: My subject
Attachments: logo.png
--------------------------------------------------------------------------------

E-Mail #0
--------------------------------------------------------------------------------
From: ["[email protected]"]
To: [email protected]
BCC: 
Subject: My subject
--------------------------------------------------------------------------------

 (RSpec::Expectations::ExpectationNotMetError)

Note that the Attachment information is missing for the listed mails, while the empty BCC header could be skipped.

A better output could be:

No matching mail was found. There were 1 mails in total.
0 of those had matching headers.
Expected
--------------------------------------------------------------------------------
From: [email protected]
To: [email protected]
Subject: My subject
Attachments: logo.png
--------------------------------------------------------------------------------

E-Mail #0
--------------------------------------------------------------------------------
From: ["[email protected]"]
To: [email protected]
Subject: My subject
Attachments: icon.png
--------------------------------------------------------------------------------

 (RSpec::Expectations::ExpectationNotMetError)