.weekYear() unexpectedly returns year (and not week)

**Describe the bug**
The weekYear() method is supposed to return the week of the year but instead it returns the year itself.

**Expected behavior**
When calling this method the following way: dayjs("2021-01-01").weekYear() it returns 2021, when the expected result would be the week of the year that day corresponds to, never the year

**Information**
- Day.js: ^1.10.3,
- Browser: Chrome 88.0.4324.150
- Time zone: UTC

Start at the weekYear() entry point and reproduce the reported dayjs("2021-01-01").weekYear() result. Check the method's existing contract and surrounding date APIs, then establish whether the returned value matches the intended meaning and add or update coverage so the expected behavior is explicit.

Written by the indexing model from the issue text.