Directly list conntrack modules instead of using a variable (#12475)

The conntrack kernel modules have no reason to be something else than
those two options, so there is no reason to have a variable.

roles/kubernetes/node/tasks/main.yml

@@ -123,7 +123,9 @@
     persistent: present
   register: modprobe_conntrack_module
   ignore_errors: true  # noqa ignore-errors
-  loop: "{{ conntrack_modules }}"
+  loop:
+    - nf_conntrack
+    - nf_conntrack_ipv4
   when:
     - kube_proxy_mode == 'ipvs'
     - modprobe_conntrack_module is not defined or modprobe_conntrack_module is ansible.builtin.failed  # loop until first success