CI: install required packages

We need the packages with xsltproc, xmllint and intltool-merge
in them.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

ci/validate.yaml

@@ -1,5 +1,10 @@
 - hosts: all
   tasks:
+    - name: Install needed packages
+      package:
+        name: ['intltool', 'libxslt', 'libxml2']
+        state: present
+      become: yes
     - name: Validate comps files
       ansible.builtin.command:
         chdir: "{{ ansible_user_dir }}/{{ zuul.project.src_dir }}"