pgp: use always_trust for encrypting to pgp-mime-text in doctest.

pgp: use always_trust for encrypting to pgp-mime-text in doctest.

This avoids the abiguously described "General error":

  S: OK GPGME-Tool 1.3.3-git73b439a ready
  C: ARMOR true
  S: OK
  C: RECIPIENT pgp-mime@invalid.com
  S: S RECIPIENT B2EDBE0E771A4B8708DD16A7511AEDA64332B6E3
  S: OK
  C: # descriptors in flight: [3]
  C: INPUT FD
  S: OK
  C: # descriptors in flight: [6]
  C: OUTPUT FD
  S: OK
  C: ENCRYPT
  S: ERR 1 General error <Unspecified source>
  C: BYE
  S: OK closing connection

I have spend some time trying to track this one down in gpgme-tool,
but without success.