libxml2: fix CVE-2016-4658

Fix use after free memory corruption involving XPointer ranges by
advancing to version 2.9.1-6.el7_9.6.

Testing

build-pkgs; build-iso (not used); create designer patch
install patch
execute sanity test
remove patch
execute sanity test

--- sanity test ---
#!/bin/python
import libxml2, sys
doc = libxml2.parseFile("/etc/firewalld/zones/public.xml")
print doc.name
---

Closes-Bug: 1954718
Signed-off-by: Joe Slater <joe.slater@windriver.com>
Change-Id: I18ca9f179b6db2f95dfd532f62195f69b29add9b

centos-mirror-tools/config/centos/distro/rpms_centos.lst

@@ -536,8 +536,8 @@ libxkbcommon-devel-0.7.1-3.el7.x86_64.rpm
 libxkbfile-1.0.9-3.el7.x86_64.rpm
 libxklavier-5.4-7.el7.x86_64.rpm
 libxklavier-devel-5.4-7.el7.x86_64.rpm
-# libxml2-2.9.1-6.el7_2.3.x86_64.rpm provided by mock
-libxml2-devel-2.9.1-6.el7_2.3.x86_64.rpm
+# libxml2-2.9.1-6.el7_9.6.x86_64.rpm provided by mock
+libxml2-devel-2.9.1-6.el7_9.6.x86_64.rpm
 libXmu-1.1.2-2.el7.x86_64.rpm
 libXpm-3.5.12-1.el7.x86_64.rpm
 libXrandr-1.5.1-2.el7.x86_64.rpm