Fixed TypeError in "ch-monitoring backup" command

[Alex-Burmak]

2023-09-05 17:35:36,155 518168 [ERROR] backup: Got error TypeError("'>=' not supported between instances of 'datetime.timedelta' and 'str'",)
Traceback (most recent call last):
  File "/opt/yandex/clickhouse-tools/lib/python3.6/site-packages/ch_tools/monrun_checks/main.py", line 77, in callback_wrapper
    result = ctx.invoke(cmd_callback, *args, **kwargs)
  File "/opt/yandex/clickhouse-tools/lib/python3.6/site-packages/click/core.py", line 754, in invoke
    return __callback(*args, **kwargs)
  File "/opt/yandex/clickhouse-tools/lib/python3.6/site-packages/ch_tools/monrun_checks/ch_backup.py", line 53, in backup_command
    check_backup_age(ch_client, backups, crit=crit_absent)
  File "/opt/yandex/clickhouse-tools/lib/python3.6/site-packages/ch_tools/monrun_checks/ch_backup.py", line 123, in check_backup_age
    if crit is not None and uptime >= crit and backup_age >= crit:
TypeError: '>=' not supported between instances of 'datetime.timedelta' and 'str'