add quotes around octal values

YAML loaders will load them as strings, providing a consistent behavior. This is also safer as JSON does not support octal values either.

roles/mariadb/tasks/mariadb.yml

@@ -32,5 +32,5 @@
     dest: /etc/mysql/my.cnf
     owner: mysql
     group: mysql
-    mode: 0600
+    mode: "0600"
   notify: restart mariadb

roles/mariadb/tasks/mysqld_exporter.yml

@@ -44,5 +44,5 @@
     dest: /etc/systemd/system/mysqld_exporter.service
     owner: root
     group: root
-    mode: 0644
+    mode: "0644"
   notify: restart mysqld_exporter