[ci] Install python3-netaddr on the controller

ansible-lint seems to have gained the ability to analyse jinja2 templates.

This patch fixes errors like:
Error: An unhandled exception occurred while running the lookup plugin 'template'.
Error was a <class 'ansible.errors.AnsibleFilterError'>, original message:
The ipaddr filter requires python's netaddr be installed on the ansible controller.

(cherry picked from commit d54b350)

.github/workflows/continuous-integration.yml

@@ -41,6 +41,7 @@ jobs:
       - name: Prepare test environment
         run: |
           sudo apt-get remove --purge -yq ansible
+          sudo apt-get install python3-netaddr
           pip3 install --upgrade pip wheel setuptools
           pip3 install --user --upgrade Jinja2 ansible ansible-lint