Don't allocate pseudo-tty

-T allows execution of the backup script by cron or similar tools.

docs/u_e-backup_restore-mysql.md

@@ -4,7 +4,7 @@
 cd /path/to/mailcow-dockerized
 source mailcow.conf
 DATE=$(date +"%Y%m%d_%H%M%S")
-docker-compose exec mysql-mailcow mysqldump --default-character-set=utf8mb4 -u${DBUSER} -p${DBPASS} ${DBNAME} > backup_${DBNAME}_${DATE}.sql
+docker-compose exec -T mysql-mailcow mysqldump --default-character-set=utf8mb4 -u${DBUSER} -p${DBPASS} ${DBNAME} > backup_${DBNAME}_${DATE}.sql
 ```
 
 ## Restore