Fix a regression in 6.8 where the 'single' headings option was not recognized.

Taken from upstream:

  https://git.savannah.gnu.org/cgit/texinfo.git/commit/?id=13a8894fe2faa45b04033d7122a8fe7939ce6aa2

diff --git a/tp/Texinfo/XS/parsetexi/end_line.c b/tp/Texinfo/XS/parsetexi/end_line.c
index 4556780052..3fc2065616 100644
--- a/tp/Texinfo/XS/parsetexi/end_line.c
+++ b/tp/Texinfo/XS/parsetexi/end_line.c
@@ -778,8 +778,8 @@ kdbinputstyle_invalid:
     case CM_headings:
       {
         if (!strcmp (line, "off") || !strcmp (line, "on")
-            || !strcmp (line, "double") || !strcmp (line, "singleafter")
-            || !strcmp (line, "doubleafter"))
+            || !strcmp (line, "single") || !strcmp (line, "double")
+            || !strcmp (line, "singleafter") || !strcmp (line, "doubleafter"))
           {
             ADD_ARG(line);
           }
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mpat.
(sdl2): Don't inherit from sdl.
(propagated-inputs-with-sdl2): Add case for sdl12-compat.
* gnu/packages/patches/sdl-libx11-1.6.patch: Remove file.
* gnu/local.mk (dist_patch_DATA): Unregister it.

Change-Id: I843d349b3d69164cc640c7db204464a51819a0df
Signed-off-by: Maxim Cournoyer &lt;maxim.cournoyer@gmail.com&gt;
</span></span></td><td>宋文武</td></tr>
<tr><td><span title='2024-08-05 00:44:43 +0300'>2024-08-05</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=3c309a7b7020a9645bfe775d9f53f43f05d076bf'>Change email of Evgeny Pisemsky.</a><span class='msg-avail'>...<span class='msg-tooltip'>* .mailmap: Add entry to Evgeny Pisemsky.
* gnu/packages/emacs-xyz.scm, gnu/packages/engineering.scm,
gnu/packages/guile-xyz.scm, gnu/packages/hardware.scm,
gnu/packages/perl.scm, gnu/packages/python-xyz.scm,
gnu/packages/sdl.scm, gnu/packages/web.scm: Adjust copyright line.

Change-Id: I9a10be1ee7cc164f18d826b51348ee26eee2ca4b
Signed-off-by: Efraim Flashner &lt;efraim@flashner.co.il&gt;
</span></span></td><td>Evgeny Pisemsky</td></tr>
<tr><td><span title='2024-07-18 11:21:34 +0100'>2024-07-18</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=843b85c42745d65c93d6af81cd3a9d835ff1f51c'>gnu: sdl2-gamecontrollerdb: Update to 0-1.9d09945.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/sdl.scm (sdl2-gamecontrollerdb): Update to 0-1.9d09945.

Change-Id: I593fdac1ae4c8e439e2b29eab5880a6acdde80bc
Signed-off-by: Christopher Baines &lt;mail@cbaines.net&gt;
</span></span></td><td>Evgeny Pisemsky</td></tr>
<tr><td><span title='2024-03-31 20:47:19 -0400'>2024-03-31</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=f7c259b2659cbd752ce5e1bcd2c2d66188295967'>gnu: sdl2: Update to 2.30.1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/sdl.scm (sdl2): Update to 2.30.1.

Change-Id: I0417cfaa0af55df63f731efad420de9f2b81a3d9
Signed-off-by: John Kehayias &lt;john.kehayias@protonmail.com&gt;
</span></span></td><td>dan</td></tr>
<tr><td><span title='2023-11-05 22:11:30 -0500'>2023-11-05</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=97f292b47f70c4744e374494cbe248ddcb139082'>gnu: sdl2: Update to 2.28.5.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/sdl.scm (sdl2): Update to 2.28.5.

Change-Id: I853776bf82e84499486d32012a9b3a4636226668
</span></span></td><td>John Kehayias</td></tr>
<tr><td><span title='2023-11-05 22:09:53 -0500'>2023-11-05</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=50521348c89140705ca157a7d77f4acda24c26c7'>gnu: sdl2: Add vulkan-loader to rpath.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/sdl.scm (sdl2)[arguments]: Append the path of libvulkan.so to
rpath.
[inputs]: Add vulkan-loader.

Signed-off-by: John Kehayias &lt;john.kehayias@protonmail.com&gt;
Change-Id: I17c8388f5f7b3bb063b79fd4981263994da129c0
</span></span></td><td>dan</td></tr>
<tr><td><span title='2023-10-27 16:33:33 +0200'>2023-10-27</span></td><td><a href='/guix/commit/gnu/packages/sdl.scm?id=2ff8de3657a5c9d0abf67bb4705251b23d97702e'>gnu: Add sdl2-gamecontrollerdb.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/sdl.scm (sdl2-gamecontrollerdb): New variable.
</span></span></td><td>Evgeny Pisemsky</td></tr>