test(pkgs_spec): update `centos-8` for `2019.2.3` release

* https://docs.saltstack.com/en/latest/topics/releases/2019.2.3.html

test/integration/v201902-py3/controls/pkgs_spec.rb

@@ -7,7 +7,7 @@ version =
     when 'amazon'
       '2019.2.2-1.el7'
     when 'centos'
-      '2019.2.2-1.el8'
+      '2019.2.3-1.el8'
     end
   when 'fedora'
     '2019.2.1rc0-3.fc31'