test: skip large cdata test on system libxml2

because distros have started backporting the fix[1] from 2.10.3 and as
a result we can't easily tell whether to expect errors or not.

backport of 0b2e41d

  [1]: https://gitlab.gnome.org/GNOME/libxml2/-/commit/c846986

test/xml/sax/test_parser.rb

@@ -402,7 +402,7 @@ def call_parse_io_with_encoding(encoding)
     end
 
     it :test_large_cdata_is_handled do
-      skip("see #2132 and https://gitlab.gnome.org/GNOME/libxml2/-/issues/200") if Nokogiri.uses_libxml?("<=2.9.10")
+      skip("see #2132 and https://gitlab.gnome.org/GNOME/libxml2/-/issues/200") if Nokogiri::VersionInfo.instance.libxml2_using_system?
 
       template = <<~EOF
         <?xml version="1.0" encoding="UTF-8"?>