Incorrect UTC offset when manipulating dayJS object (DST/STD change)

[georgehrke]

Describe the bug
In the code-snipped below, a new dayjs object is initialized and set to Asia/Tel_Aviv. This timezone is different from my own one, which is Europe/Berlin.

The object is set to the 31st of October 2021. On that day, Israel (and the majority of the remaining world, which is observing DST) will change back from Daylight Savings Time to Standard Time.

2 am correctly appears twice. However, the UTC offset incorrectly does not change. Instead of printing 02:00+03:00 twice, it should print 02:00+03:00 once, followed by 02:00+02:00

let day = dayjs('2021-10-31').tz('Asia/Tel_Aviv').startOf('day');
console.log(day.format('HH:mmZ'));
day = day.add(1, 'hour');
console.log(day.format('HH:mmZ'));
day = day.add(1, 'hour');
console.log(day.format('HH:mmZ'));
day = day.add(1, 'hour');
console.log(day.format('HH:mmZ'));
day = day.add(1, 'hour');
console.log(day.format('HH:mmZ'));

Expected behavior

Actual	Expected
00:00+03:00	00:00+03:00
01:00+03:00	01:00+03:00
02:00+03:00	02:00+03:00
02:00+03:00	02:00+02:00
03:00+03:00	03:00+02:00

Information

• Day.js v1.10.6
• OS: macOS Big Sur (11.5.2)
• Browser: Google Chrome 92.0.4515.159 (Official Build) (x86_64)
• Time zone: Europe/Berlin (we are currently on UTC+02:00)