distro/test: update CA certificates for CentOS

On CentOS 7, the base image has an outdated LetsEncrypt certificate.

distro/tests/ansible-roles/obs_repos/tasks/CentOS.yaml

 ---
 # SPDX-License-Identifier: GPL-3.0-or-later
+- name: update CA certificates
+  yum:
+    name: ca-certificates
+    state: latest
+
 - name: Install EPEL
   yum:
     name: epel-release