TimeZone issue on Dayjs-values initially created before DST

[anderskjeldsen]

** Description of the problem **
Running the current typescript code:

printDates() {
var timeAfterDaylightSavings = new Date(2024, 2, 31, 18, 0, 0, 0);
var startOfDayWithDST = dayjs.tz(timeAfterDaylightSavings, "Europe/Oslo").startOf('day');
var currentTime = startOfDayWithDST;
for(let i = 0; i < 4; i++) {
this.printDate(currentTime);
currentTime = currentTime.add(1, 'hour');
}
}

printDate(d: dayjs.Dayjs) {
return console.log("Date: " + d.format('YYYY-MM-DD HH:mm:ss') + ", UTC date: " + d.toDate().toISOString());
}

It prints the following:

TZ date: 2024-03-31 00:00:00, UTC date: 2024-03-30T23:00:00.000Z
TZ date: 2024-03-31 01:00:00, UTC date: 2024-03-31T00:00:00.000Z
TZ date: 2024-03-31 03:00:00, UTC date: 2024-03-31T02:00:00.000Z <--- wrong
TZ date: 2024-03-31 04:00:00, UTC date: 2024-03-31T03:00:00.000Z

The third line is wrong. DST happens at 02:00 local time and therefore local time jumps from 1:59 to 3. This is correct. However, UTC time should not skip an extra hour as well.

Expected behavior
I write a similar snippet using Java and ZonedDateTime, and it appears to print the correct values (not the same date formats):
TZ date: 2024-03-31T00:00+01:00[Europe/Oslo], UTC date: 30 Mar 2024 23:00:00 GMT
TZ date: 2024-03-31T01:00+01:00[Europe/Oslo], UTC date: 31 Mar 2024 00:00:00 GMT
TZ date: 2024-03-31T03:00+02:00[Europe/Oslo], UTC date: 31 Mar 2024 01:00:00 GMT
TZ date: 2024-03-31T04:00+02:00[Europe/Oslo], UTC date: 31 Mar 2024 02:00:00 GMT

Also, doing it the other way around by adding hours to the Date objects and creating a new Dayjs object from that everytime works (append the following code inside the printDates function):
let currentDate = startOfDayWithDST.toDate();
for(let i = 0; i < 4; i++) {
currentTime = dayjs.tz(currentDate, "Europe/Oslo");
this.printDate(currentTime);
currentDate.setHours(currentDate.getHours() + 1)
}

TZ Date: 2024-03-31 00:00:00, UTC date: 2024-03-30T23:00:00.000Z
TZ Date: 2024-03-31 01:00:00, UTC date: 2024-03-31T00:00:00.000Z
TZ Date: 2024-03-31 03:00:00, UTC date: 2024-03-31T01:00:00.000Z
TZ Date: 2024-03-31 04:00:00, UTC date: 2024-03-31T02:00:00.000Z

Information

• Day.js Version: v1.11.10
• OS: Any (mostly tested on Ubuntu and Mac)
• Browser: Chrome (probably others)
• Time zone: Europe/Oslo