Getting invalid time for partial time

**Describe the bug**
This works well
```
const ts = "15:00:00"
const timeString = dayjs(ts, 'HH:mm:ss').format('HH:mm:ss');

```
But if
```
const ts = "15:00"
const timeString = dayjs(ts, 'HH:mm:ss').format('HH:mm:ss');

```
This gives invalid date if it doesn't matches with the parse format

**Expected behavior**
It should parse partial string correctly as moment does

**Information**
- Day.js Version [1.11.7]
- OS: [iOS]
- Browser [node: 18]
- Time zone: [GMT +5:30 ]

@iamkun