Fix comment about `matrix_mautrix_whatsapp_database_*` variables

Was renamed in 087dbe4ddc

It is unclear to me if there is anything you actually need to adjust with these variables. It looks like that is done automatically in `matrix_servers`.

roles/matrix-bridge-mautrix-whatsapp/defaults/main.yml

@@ -42,7 +42,7 @@ matrix_mautrix_whatsapp_appservice_bot_username: whatsappbot
 #
 # To use Postgres:
 # - change the engine (`matrix_mautrix_whatsapp_database_engine: 'postgres'`)
-# - adjust your database credentials via the `matrix_mautrix_whatsapp_postgres_*` variables
+# - adjust your database credentials via the `matrix_mautrix_whatsapp_database_*` variables
 matrix_mautrix_whatsapp_database_engine: 'sqlite'
 
 matrix_mautrix_whatsapp_sqlite_database_path_local: "{{ matrix_mautrix_whatsapp_data_path }}/mautrix-whatsapp.db"