Add subject to dummy thread roots

Sometimes, when adding dummy roots, Gnus displays the thread subject
on the first message:

(emacs-devel, fetched from archive.lwn.net)
                     ┌◈
    10:31            ├► martin rudalics          Re: emacs rendering comparisson between emacs23 and emacs26.3
    14:07            │├► Dmitry Gutov
    14:35            ││├► Dmitry Gutov
    14:45            ││╰► martin rudalics
    13:47            │╰► Alan Mackenzie
    14:45            ┆ ╰► martin rudalics

And sometimes it doesn't:

(bug-gnu-emacs, fetched from news.gmane.io)
                     ┌◈
    02:08            ├► Juri Linkov
    05:33            ╰► Stefan Monnier

Adding %S to the dummy line-format will cause the subject to appear
twice in the first situation (on the dummy root, then on the first
message); not great, but better than not knowing what the topic is.

1 files changed, 1 insertions, 1 deletions

diff --git a/.gnus b/.gnus
index aa198e0..1cbb829 100644
--- a/.gnus
+++ b/.gnus
@@ -16,7 +16,7 @@
       '((nntp "archive.lwn.net")
         (nntp "news.gmane.io"))
       gnus-summary-line-format "%*%U%R  %-16,16&user-date; %B%-23,23n  %s\n"
-      gnus-summary-dummy-line-format "                    ┄┐\n"
+      gnus-summary-dummy-line-format "                     ┌◈                          %S\n"
       gnus-summary-make-false-root 'dummy
       gnus-sum-thread-tree-root "┌◈ "
       gnus-sum-thread-tree-false-root "┄┐ "