roles: strict truthy values

According to Ansible we can use yes, true, True, "or any quoted st-
ring" for a boolean true, but ansible-lint wants us to use either
true or false.

See: https://chronicler.tech/red-hat-ansible-yes-no-and/

roles/common/tasks/fail2ban.yml

@@ -20,6 +20,6 @@
     - restart fail2ban
 
 - name: Start and enable fail2ban service
-  ansible.builtin.systemd: name=fail2ban state=started enabled=yes
+  ansible.builtin.systemd: name=fail2ban state=started enabled=true
 
 # vim: set sw=2 ts=2: