Bump libxml2 from 2.10.3 to 2.12.6

This commit updates the libxml2 component from 2.10.3 to 2.12.6. In
addition to various bug fixes, this also addresses the following
security vulnerabilities:

- CVE-2023-28484
- CVE-2023-29469
- CVE-2024-25062

configs/components/libxml2.rb

@@ -1,6 +1,6 @@
 component "libxml2" do |pkg, settings, platform|
-  pkg.version '2.10.3'
-  pkg.sha256sum '5d2cc3d78bec3dbe212a9d7fa629ada25a7da928af432c93060ff5c17ee28a9c'
+  pkg.version '2.12.6'
+  pkg.sha256sum '4709e55f59dfa2acdbf1d3c06f1113f8dda2b6012e4f30c2814a4d66c4e92bd2'
 
   libxml2_version_y = pkg.get_version.gsub(/(\d+)\.(\d+)\.(\d+)/, '\1.\2')
   pkg.url "https://download.gnome.org/sources/libxml2/#{libxml2_version_y}/libxml2-#{pkg.get_version}.tar.xz"