Got 'Etc/Unknown' after calling dayjs.tz.guess

**Describe the bug**
Got 'Etc/Unknown' after calling dayjs.tz.guess

**Expected behavior**
A right time zone.
Under what circumstances would this result be obtained?

**Information**
- Day.js Version [^1.11.7]

Start by tracing the dayjs.tz.guess entry point and the timezone-detection behavior used by Day.js 1.11.7. Reproduce the reported result in an environment where it occurs, determine the circumstances that produce Etc/Unknown, and verify the result is either corrected or clearly documented.

Written by the indexing model from the issue text.