bug#67559: 29.1; Fix indentation in code example of optional arguments

[Eli Zaretskii]

> From: Xiyue Deng <manphiz@gmail.com>
> Date: Thu, 30 Nov 2023 17:45:57 -0800
> 
> The code example in the optional arguments section seems a little off in
> indentation according to Elisp convention.  The attached patch tries to
> improve it.

Thanks, but "git am" rejects this patch with the following message:

  Line longer than 78 characters in commit message
  Commit aborted; please see the file CONTRIBUTE

Please fix the commit log message (I think the problem is in the
Subject line, actually) and resubmit.