roles/mariadb: install packages in single transaction

Using a list we can install these in a single apt transaction. Also
use the newer task format.

roles/mariadb/tasks/main.yml

@@ -49,10 +49,10 @@
     - mariadb
 
 - name: Install mariadb-server
-  ansible.builtin.apt: name={{ item }} state=present cache_valid_time=3600
+  ansible.builtin.apt:
-  loop:
+    name: ['mariadb-server', 'python3-pymysql']
-    - mariadb-server
+    state: present
-    - python3-pymysql # for ansible
+    cache_valid_time: 3600
   tags: mariadb, packages
 
 - name: Create system my.cnf