Steps to reproduce:

1. Create an item with the JavaScript preprocessing step with the following parameter:

var timestampWithTimezone = "2024-02-20T13:16:00+0100";
//var timestampWithTimezone = "2024-02-20T13:16:00+01:00";
var date = new Date(timestampWithTimezone);
var unixTime = date.getTime() / 1000;
return unixTime;

1. Test it.

Result:
Wrong unixtime is returned:
Returned 1708074960 which converts to 2024-02-16T09:16:00
Different inputs have different results: 

• 2024-02-20T13:16:00+0100 - doesn't work
• 2024-02-20T13:16:00+01:00 - works as expected

Expected:
Correct conversion to 2024-02-20T13:16:00+0100

According to the:
https://github.com/svaarala/duktape/blob/master/doc/datetime.rst
and
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date#date_time_string_format

We should support both cases.