error[preamble-author]: authors in the preamble must match the expected format
 --> input.md:5:8
  |
5 | author: John Doe (@johndoe)a, Jenny Doe (@jen)
  |        ^^^^^^^^^^^^^^^^^^^^^ unrecognized author
  |
  = help: Try `Random J. User (@username) <test@example.com>` for an author with a GitHub username plus email.
  = help: Try `Random J. User (@username)` for an author with a GitHub username.
  = help: Try `Random J. User <test@example.com>` for an author with an email.
  = help: Try `Random J. User` for an author without contact information.