Fixes build with Python >= 3.6:

------
Making all in libgnomeui
make[2]: Entering directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
  GEN    stamp-gnome-marshal.h
  GEN    stamp-gnometypebuiltins.h
INFO: Reading ./gnome-marshal.list...
  GEN    gnome-marshal.h
Traceback (most recent call last):
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 688, in <module>
    process_file(fname)
  File "/gnu/store/...-glib-2.54.2-bin/bin/glib-mkenums", line 420, in process_file
    line = curfile.readline()
  File "/gnu/store/...-python-3.6.3/lib/python3.6/codecs.py", line 321, in decode
    (result, consumed) = self._buffer_decode(data, self.errors, final)
UnicodeDecodeError: 'utf-8' codec can't decode byte 0xf1 in position 1009: invalid continuation byte
make[2]: *** [Makefile:1109: stamp-gnometypebuiltins.h] Error 1
make[2]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5/libgnomeui'
make[1]: *** [Makefile:369: all-recursive] Error 1
make[1]: Leaving directory '/tmp/guix-build-libgnomeui-2.24.5.drv-0/libgnomeui-2.24.5'
make: *** [Makefile:296: all] Error 2
------

Patch copied from upstream source repository:

https://git.gnome.org/browse/libgnomeui/commit/?id=30334c28794ef85d8973f4ed0779b5ceed6594f2

From 30334c28794ef85d8973f4ed0779b5ceed6594f2 Mon Sep 17 00:00:00 2001
From: Colin Walters <walters@verbum.org>
Date: Mon, 7 Aug 2017 13:15:26 -0400
Subject: [PATCH] gnome-scores.h: Convert to UTF-8

The new Python `glib-mkenums` barfs on ISO-8859-1 input.
---
 libgnomeui/gnome-scores.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/libgnomeui/gnome-scores.h b/libgnomeui/gnome-scores.h
index 911b12d1..4e641d22 100644
--- a/libgnomeui/gnome-scores.h
+++ b/libgnomeui/gnome-scores.h
@@ -27,7 +27,7 @@
  * "High Scores" Widget 
  *
  * AUTHOR: 
- * Horacio J. Peña <horape@compendium.com.ar>
+ * Horacio J. Peña <horape@compendium.com.ar>
  *
  * This is free software (under the terms of the GNU LGPL)
  *
path'>path: <a href='/guix/log/?id=97f2f03c62477283c368471e7d9daa87cd6dbdc4'>root</a>/<a href='/guix/log/etc?id=97f2f03c62477283c368471e7d9daa87cd6dbdc4'>etc</a>/<a href='/guix/log/etc/snippets?id=97f2f03c62477283c368471e7d9daa87cd6dbdc4'>snippets</a>/<a href='/guix/log/etc/snippets/tempel?id=97f2f03c62477283c368471e7d9daa87cd6dbdc4'>tempel</a></div><div class='content'><table class='list nowrap'><tr class='nohover'><th class='left'>Age</th><th class='left'>Commit message (<a href='/guix/log/etc/snippets/tempel?id=97f2f03c62477283c368471e7d9daa87cd6dbdc4&amp;showmsg=1'>Expand</a>)</th><th class='left'>Author</th></tr>
<tr><td><span title='2023-10-15 12:28:19 +0200'>2023-10-15</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=ef026e68fe58ed3be216c76f7c5f008893ed3095'>etc: snippets: Do not match unintended quotes.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2023-04-19 20:12:22 -0400'>2023-04-19</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=7cb21556b6031c9f7e187329b6663768425aa850'>snippets: tempel: Simplify git-commit-mode detection.</a><span class='msg-avail'>...</span></td><td>Nicolas Graves</td></tr>
<tr><td><span title='2023-03-05 08:17:58 +0100'>2023-03-05</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=d92ec2f2812c76b23aab778e26708cf353542ae9'>etc: Default to variables in tempel's git-reference... et al.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2022-12-27 12:38:05 +0400'>2022-12-27</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=8f93a1e01a879ae026678dd92c18e2a2a49be540'>snippets: Remove unwanted git-commit-mode invocation.</a><span class='msg-avail'>...</span></td><td>Andrew Tropin</td></tr>
<tr><td><span title='2022-10-22 14:16:13 +0200'>2022-10-22</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=85aff4de30686359ffb50845eb0930c0a18dc8ba'>snippets: Harden for review activity.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2022-10-06 21:16:46 +0200'>2022-10-06</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=5e63e51afee0f674ff2ac961e3103011f53035cd'>snippets: Fix move.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2022-10-06 21:16:46 +0200'>2022-10-06</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=da281417cc381374345dd404b2f10b4cb07a87d2'>snippets: tempel: Reformat.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2022-10-06 21:16:45 +0200'>2022-10-06</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=980c34853e1020018df3a0c04753ea46d880e9a7'>snippets: tempel: Fix calls to mapconcat.</a><span class='msg-avail'>...</span></td><td>Liliana Marie Prikler</td></tr>
<tr><td><span title='2022-09-26 23:29:36 +0200'>2022-09-26</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=b6274a20e8e99fa6287264289da42ed364fc976c'>etc: Add tempel snippet move.</a><span class='msg-avail'>...</span></td><td>Nicolas Graves</td></tr>
<tr><td><span title='2022-08-30 11:50:15 +0200'>2022-08-30</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=0928b82070d495a413a1df873cfc817b673cd4d1'>etc: Add tempel snippet for :phases.</a><span class='msg-avail'>...</span></td><td>Nicolas Graves</td></tr>
<tr><td><span title='2022-08-30 11:50:14 +0200'>2022-08-30</span></td><td><a href='/guix/commit/etc/snippets/tempel?id=c4acaf412064568a546034871a9e0d3888aa7937'>etc: Add tempel snippets.</a><span class='msg-avail'>...</span></td><td>Nicolas Graves</td></tr>