Schedule format with forward slash (/) not supported

Maybe I missed something, but it seems like I can't set a cron schedule that includes a forward slash like so:
```
*/10 * * * *
```
this should execute the cronjob at every 10th minute, so at :00, :10, :20, :30, :40 and :50.
I used the following command to update the crontask:
```
ee cron update 1 --schedule="*/10 * * * *"
```
and got the following error:
`Error: Schedule format should be same as Linux cron or schedule helper syntax(Check help for this)`

Incidentally, it is not possible to set multiple minutes either:
```
ee cron update 5 --schedule="0,10,20,30,40,50 * * * *"
```

The interesting part is when it comes to reading existing cronjobs. Running `ee cron list website.com` gives the following output:
```
+----+-------------+-------------------------------------+----------------+
| id | site_url | command | schedule |
+----+-------------+-------------------------------------+----------------+
| 5 | website.com | sh -c 'wp cron event run --due-now' | 0 5/10 * * * * |
+----+-------------+-------------------------------------+----------------+
```
The issue is that `0 5/10 * * * *` itself is not a properly formatted cron schedule expression, at least when validated with a website called [crontab.guru](https://crontab.guru/).
I suspect it should actually be `5/10 * * * *`, but then again this cannot be set.
So changing an existing cron schedule makes it impossible to go back…

首先使用 `*/10 * * * *` 和 `0,10,20,30,40,50 * * * *` 运行 `ee cron update` 命令重现问题，然后检查 `ee cron list` 背后的调度处理逻辑。将接受的输入与标准的五字段 Linux cron 语法以及显示的 `0 5/10 * * * *` 值进行比较。当可以设置包含斜杠和逗号的调度，并且现有调度能够以有效的 cron 格式往返传递时，即表示完成。

由索引模型根据 Issue 内容生成。