bug#72196: 30.0.60; gnus-search-indexed-search-command passes incorrect maildir argument to mu

hi,
i am also hitting this bug with mu + nnmaildir, and i've been using a similar workaround for about a month now.  it's still broken in my emacs 30.2.

here's the workaround from my config:

#+begin_src elisp
  (cl-defmethod gnus-search-run-search :around
    ((engine gnus-search-indexed) server query groups)
    (cl-call-next-method engine server query
                         (mapcar #'gnus-group-short-name groups)))
#+end_src

it strips server prefix ("nnmaildir+server:inbox" -> "inbox") before handing
groups to mu's maildir: filter.  it's the same fix as the original report, but
using the built in ~gnus-group-short-name~ instead of a regex.

works for me!

thanks,
daniel watson