Tests (and CI) failing

[WhyNotHugo]

Tests are failing because a lot of the output khal generates has changed.

Example: https://github.com/pimutils/khal/actions/runs/3573830145/jobs/6008353776#step:6:2828

The difference seems to be that VALUE= is omitted on dates.

  -  b'BEGIN:VEVENT\r\nSUMMARY:\xc3\x84wes\xc3\xb6me Event\r\nDTSTART;VALUE=DATE-TI'
  ?                                                                  ^^^^^^^^^ ^^^^
  +  b'BEGIN:VEVENT\r\nSUMMARY:\xc3\x84wes\xc3\xb6me Event\r\nDTSTART:20140216T0800'
  ?                                                                  ^^^^^^^^^ ^^^^

I believe this is due to recent changes in the icalendar library. I'm fairly certain this is perfectly valid as per the icalendar spec, but I want to double check before blindly updating all tests to pass.

[WhyNotHugo]

Cause: collective/icalendar#479

[WhyNotHugo]

Context: collective/icalendar#318

[WhyNotHugo]

https://www.rfc-editor.org/rfc/rfc5545#section-3.3.5

Example: The following represents July 14, 1997, at 1:30 PM in New
York City in each of the three time formats, using the "DTSTART"
property.

   DTSTART:19970714T133000                   ; Local time
   DTSTART:19970714T173000Z                  ; UTC time
   DTSTART;TZID=America/New_York:19970714T133000

The new output is perfectly valid; it's safe to just update all the tests.