dayjs.tz() with day() make a confusing format() output

**Describe the bug**
when set default timezone, and set the day of the week , get a confusing format() output
```js
dayjs.tz.setDefault("Europe/London");

dayjs.tz('2023-02-10 14:00:00').day(3).format() // '2023-02-08T14:00:00Z'
dayjs.tz(dayjs.tz('2023-02-10 14:00:00')).day(3).format() // '2023-02-08T06:00:00Z'
dayjs.tz(dayjs.tz(dayjs.tz('2023-02-10 14:00:00'))).day(3).format() // '2023-02-08T06:00:00Z'
```

**Expected behavior**

**Playground**
https://codesandbox.io/s/focused-cohen-mkylpd

**Information**
- Day.js Version v1.11.7
- OS: windows10
- Browser chrome 109
- Time zone: Asia/Shanghai

Start by reproducing the three examples in the linked CodeSandbox with Day.js v1.11.7 and the reported time zones. The issue does not name source files or tests and leaves Expected behavior blank, so establish the intended output before tracing the timezone and day() behavior. Done means the intended behavior is documented and covered by a regression test.

Written by the indexing model from the issue text.