doc: fix indentation of refStorage item in git-config(1)

doc: fix indentation of refStorage item in git-config(1)

Commit 5a12fd2a8c (doc: change the markup of paragraphs following a
nested list item, 2025-09-27) converted the list of items in
config/extensions.adoc into a definition list. This caused a small
regression in the indentation of one item, but only when built with
AsciiDoctor. You can see the problem with:

  $ ./doc-diff --asciidoctor 5a12fd2a8c^ 5a12fd2a8c
  --- a/c44beea485f0f2feaf460e2ac87fdd5608d63cf0-asciidoctor/home/peff/share/man/man1/git-config.1
  +++ b/5a12fd2a8c850df311aa149c9bad87b7cb002abb-asciidoctor/home/peff/share/man/man1/git-config.1
  @@ -3128,9 +3128,9 @@ CONFIGURATION FILE
                  •   reftable for the reftable format. This format is
                      experimental and its internals are subject to change.

  -               Note that this setting should only be set by git-init(1) or git-
  -               clone(1). Trying to change it after initialization will not work
  -               and will produce hard-to-diagnose issues.
  +           Note that this setting should only be set by git-init(1) or git-
  +           clone(1). Trying to change it after initialization will not work and
  +           will produce hard-to-diagnose issues.

              relativeWorktrees
                  If enabled, indicates at least one worktree has been linked with

(along with many other changes which are correctly fixing what
5a12fd2a8c intended to fix). The "Note" paragraph should remain aligned
with the bullet points, as they are left-aligned with the rest of the
definition text.

The confusion comes from a paragraph following a list item (ironically,
the same case that 5a12fd2a8c was solving!). We can solve it by adding
"--" block markers around the nested list. We couldn't have done that
before 5a12fd2a8c because before then our list was nested inside another
set of block markers, something that AsciiDoctor has trouble with. But
now that we are a top-level definition list, it is OK to do so (and in
fact, you can see that commit already made a similar adjustment for the
worktreeConfig entry).

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>