Prevent a memory leak in call-channel, which otherwise would cause a
test failure in file-transfer-channel.c.

Taken from upstream:
https://gitlab.freedesktop.org/telepathy/telepathy-glib/commit/2e8b2cc0db09b781d99e3755bb6d01548037fe7b

diff --git a/telepathy-glib/call-channel.c b/telepathy-glib/call-channel.c
index 8ed76323be32f83c5f4d6045a50bc1698d8093fd..2a1fa203d4be9f0c8b99344225f4ba9900666ffc 100644
--- a/telepathy-glib/call-channel.c
+++ b/telepathy-glib/call-channel.c
@@ -525,6 +525,8 @@ update_call_members (TpCallChannel *self,
 
   _tp_channel_contacts_queue_prepare_async ((TpChannel *) self,
       contacts, update_call_members_prepared_cb, data);
+
+  g_ptr_array_unref (contacts);
 }
 
 static void
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<tr><td><span title='2017-06-07 15:58:16 -0400'>2017-06-07</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=94db92f78ec9c849f9c8da05d4d35356909f9fbe'>artwork: Use a descriptive name for the source directory.</a><span class='msg-avail'>...</span></td><td>Leo Famulari</td></tr>
<tr><td><span title='2015-05-07 23:11:23 +0200'>2015-05-07</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=cf2abac8ec07ca421393df755211779b60739ae6'>artwork: Update to latest version.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
<tr><td><span title='2015-02-24 23:43:03 +0100'>2015-02-24</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=a4d8c40f7d3d5002a307b80cfe516474ea10d19f'>artwork: Update to latest GRUB image.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>
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<tr><td><span title='2014-11-12 14:28:36 +0100'>2014-11-12</span></td><td><a href='/guix/commit/gnu/artwork.scm?id=84dfb4582121480cec7a8cfb73725ef006b747b5'>gnu: Introduce (gnu artwork) module.</a><span class='msg-avail'>...</span></td><td>Ludovic Courtès</td></tr>