week使用没有到达预期效果，看起来可能是个bug

取week的时候，日期错误，例如`dayjs().week(1)`，结果错误
`dayjs("2022-8-8").week(1).format("YYYY-MM-DD") //2021-12-27 `
`dayjs("2022-8-9").week(1).format("YYYY-MM-DD") //2021-12-28`

Start by reproducing the two dayjs().week(1) examples from the issue and inspect the week-handling entry point. Determine the expected week-1 dates for the supplied inputs, then verify that the behavior is corrected and covered by a regression test.

Written by the indexing model from the issue text.