This test fails because it expects a MIME type "Content-Type: image/gif"
whereas that provided by libmagic is "Content-Type: image/gif; charset=binary"
Presumably the test was written against a different version.
--- aegis-4.24/test/02/t0228a-matt.sh	2008-03-14 07:19:27.000000000 +0100
+++ aegis-4.24/test/02/t0228a-matt.sh	2014-01-27 09:43:44.000000000 +0100
@@ -147,7 +147,8 @@
 SCRIPT_NAME=/cgi-bin/aeget \
 PATH_INFO=icon/rss.gif \
 QUERY_STRING= \
-$bin/aeget > rss.served.gif 2>&1
+$bin/aeget \
+| sed -e 's%^Content-Type: image/gif; charset=binary%Content-Type: image/gif%' > rss.served.gif 2>&1
 if test $? -ne 0 ; then fail; fi
 
 # Compare the expected and the actual received file.
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<tr><td><span title='2022-08-14 02:00:00 +0200'>2022-08-14</span></td><td><a href='/guix/commit/gnu/packages/upnp.scm?id=367b045c5551a11d38ceb816bdee5155b78baea8'>gnu: libupnp: Update to 1.14.13.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/upnp.scm (libupnp): Update to 1.14.13.
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<tr><td><span title='2022-05-22 02:00:00 +0200'>2022-05-22</span></td><td><a href='/guix/commit/gnu/packages/upnp.scm?id=9d4d2fd5cc4b75891f0e29d368ef70e7ccc0dbf1'>gnu: readymedia: Remove input labels.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/upnp.scm (readymedia)[native-inputs, inputs]:
Remove input labels.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>
<tr><td><span title='2022-05-22 02:00:00 +0200'>2022-05-22</span></td><td><a href='/guix/commit/gnu/packages/upnp.scm?id=4e0d811e679fb97daa90f3c2764974b6fbdbf1bb'>gnu: readymedia: Update to 1.3.1.</a><span class='msg-avail'>...<span class='msg-tooltip'>* gnu/packages/upnp.scm (readymedia): Update to 1.3.1.
[arguments]: Don't explicitly return #t from phases.
</span></span></td><td>Tobias Geerinckx-Rice</td></tr>