use native list of python packages

tasks/prepare.yml

@@ -15,10 +15,9 @@
 
   - name: Install python dependencies
     pip:
-      name: "{{ item }}"
+      name:
+        - psycopg2
       state: present
-    with_items:
-      - psycopg2
   become: True
   become_user: root
   when: postgres_repository_enabled