free busy sheduling wrongly handles timezone

[odzhychko]

Steps to reproduce

1. Under "Calendar settings > General" select a timezone different from your browser/OS
   • e.g. browser/OS has "Berlin" and "Tokyo" in settings
2. Start creating an event
3. Add an attendee
4. Use "Find a time"

Expected behavior

Time of "Selected slot" (11AM - 1PM in the screenshot) matches with the time of the event (4AM - 6AM).

Actual behavior

Calendar app version

6.5.2

CalDAV-clients used

No response

Browser

No response

Client operating system

No response

Server operating system

No response

Web server

None

Database engine version

None

PHP engine version

None

Nextcloud version

No response

Updated from an older installed version or fresh install

None

List of activated apps

Nextcloud configuration

Web server error log

Log file

Browser log

Additional info

Similar issue as in #8653