dayjs not parsing german date string

dayjs is not able to parse a date string with this format: DD.MM.YYYY (2-digits day.2-digits month.4-digits year).

Given the date string "22.04.2022", dayjs tells me it is an invalid date.

Example:

```

dayjs.locale('de')
console.log(dayjs().locale()) <!-- Output: de -->
console.log(dayjs('22.04.2022')) <!-- Output: M {$L: 'de', $d: Invalid Date, $x: {…}, $y: NaN, $M: NaN, …} -->

```

Start with the provided reproduction for "22.04.2022" and locate Day.js's date-string parsing and German locale tests or entry points. Determine how this format is expected to be supported, add a regression case for the example, and run the relevant test suite to confirm the string is no longer treated as invalid.

Written by the indexing model from the issue text.