Timezone conversion is broken when not using DST Time

[matthieutirelli-pro]

Describe the bug
DST not working in dayjs

Expected behavior
It seems that DST has some problem converting times with dayjs :

dayjs("2021-10-30").set("hour", 18).set("minute", 42).tz("Europe/Paris").toISOString()
'2021-10-30T16:42:00.000Z'

It's correct, the 30th of october 2021, we are now on daylight saving time ( DST ) at Paris timezone ( UTC+1 ) we substract 2 hours to get the UTC TIME, 16:42 is correct.

dayjs("2021-10-31").set("hour", 18).set("minute", 42).tz("Europe/Paris").toISOString()
'2021-10-31T18:42:00.000Z'

Is incorrect, the 31th of october 2021, DST will be over, but we should still substract 1 hour to get the UTC Time ( 17:42 )

Seems that no matter which timezone we use, when we are not in DST, the offset is not done in reference with UTC.

dayjs("2021-10-31").set("hour", 18).set("minute", 42).tz("Asia/Tel_Aviv").toISOString()
'2021-10-31T18:42:00.000Z'


dayjs("2021-10-30").set("hour", 18).set("minute", 42).tz("Asia/Tel_Aviv").toISOString()
'2021-10-30T16:42:00.000Z'

Seems to be kind of the same problem referenced here : #1622

Information

• Day.js Version 1.10.7
• OS: MacOS
• Browser : Chrome 93.0.4577.63 (Build officiel) (x86_64)
• Time zone: UTC+1 ( Europe/Paris )