vault: Use FQCN for ansible.builtin

Use Fully Qualified Collection Name (FQCN) for ansible builtins. This is
ansible.builtin.set_fact instead of set_fact for example and aplies for
all actions that are part of ansible.builtin.

All the replaced ansible.builtins:
  assert, command, copy, debug, fail, fetch, file, import_playbook,
  import_tasks, include_role, include_tasks, include_vars, package,
  set_fact, shell, slurp, stat, systemd

tests/vault/env_setup.yml

@@ -1,10 +1,10 @@
 ---
   # Tasks executed to ensure a sane environment to test IPA Vault module.
   - name: Ensure environment is clean.
-    import_tasks: env_cleanup.yml
+    ansible.builtin.import_tasks: env_cleanup.yml
 
   - name: Create private/public key pair.
-    shell:
+    ansible.builtin.shell:
       cmd: |
         openssl genrsa -out "{{ item }}private.pem" 2048
         openssl rsa -in "{{ item }}private.pem" -outform PEM -pubout -out "{{ item }}public.pem"
@@ -17,7 +17,7 @@
     - B_
 
   - name: Copy files to target host.
-    copy:
+    ansible.builtin.copy:
       src: "{{ playbook_dir }}/{{ item }}"
       dest: "{{ ansible_facts['env'].HOME }}/{{ item }}"
       mode: 0644