VTODO entries with UTC time are not showing up in users timezone

[juliushaertl]

Steps to reproduce

1. Have a VTODO entry like this

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//Sabre//Sabre VObject 4.3.0//EN
CALSCALE:GREGORIAN
BEGIN:VTODO
UID:deck-card-1
DTSTAMP:20200915T081957Z
DUE:20200917T140000Z
RELATED-TO:deck-stack-1
STATUS:NEEDS-ACTION
CATEGORIES:zzzz,aaaa
SUMMARY:Beispielaufgabe 3
DESCRIPTION:
END:VTODO
END:VCALENDAR

Expected behaviour

DUE:20200917T140000Z should be converted to the users timezone.

Actual behaviour

The due date is shown at 14:00 no matter which timezone the user is in.

This works as expected in calendar for example.

Specification

From https://www.kanzaki.com/docs/ical/dateTime.html:

FORM #2: DATE WITH UTC TIME

The date with UTC time, or absolute time, is identified by a LATIN CAPITAL LETTER Z suffix character (US-ASCII decimal 90), the UTC designator, appended to the time value. For example, the following represents January 19, 1998, at 0700 UTC:

DTSTART:19980119T070000Z

The TZID property parameter MUST NOT be applied to DATE-TIME properties whose time values are specified in UTC.

Server configuration

Nextcloud version: 20

Tasks version: latest master

Omitted the rest of the server configuration since it seems irrelevant for this issue, however I'm happy to provide it of course if needed.

[raimund-schluessler]

Requires #1739

[AlphaCraft9658]

This issue is still kinda there, unless it has been fixed in Nextcloud 29, which I don't have yet. When creating a task, it doesn't show the due-date and time in the correct time zone until I refresh the page. A minor but annoying bug.