dayjs('99', 'MM').isValid() returns true

**Describe the bug**
As stated, `dayjs('99', 'MM')` creates a valid date in 1999 so `isValid` returns true.

**Expected behavior**
I would expect it to return false.

**Information**
- Day.js Version 1.11.3
- OS: Windows
- Browser: Chrome
- Time zone: GMT +9 Tokyo

Start by reproducing the reported entry point, dayjs('99', 'MM').isValid(), using Day.js 1.11.3 or the current version. Trace how the formatted month input is parsed and determine whether this input should be rejected; done means isValid() returns false for this case without breaking valid formatted dates.

Written by the indexing model from the issue text.