Switch from `postgres_backup_databases` to `postgres_backup_databases_auto`

Ref: https://github.com/mother-of-all-self-hosting/ansible-role-postgres-backup/pull/6

Related to a445f8a5ae

group_vars/matrix_servers

@@ -4246,7 +4246,7 @@ postgres_backup_connection_password: "{{ postgres_connection_password if postgre
 postgres_backup_postgres_data_path: "{{ postgres_data_path if postgres_enabled else '' }}"
 postgres_backup_postgres_role_include_name: galaxy/postgres
 
-postgres_backup_databases: "{{ postgres_managed_databases | map(attribute='name') if postgres_enabled else [] }}"
+postgres_backup_databases_auto: "{{ postgres_managed_databases | map(attribute='name') if postgres_enabled else [] }}"
 
 ########################################################################
 #                                                                      #