Fixed duplicate RECURRENCE-ID when expanding events

[dozed]

Fixes #394

There is an issue with Xandikos: when searching for the events a 500 Internal Server Error is returned. This might need some investigation.

[tobixen]

  File "/home/runner/work/caldav/caldav/.tox/py/lib/python3.10/site-packages/xandikos/icalendar.py", line 1039, in asutc
153
    return dt.astimezone(pytz.utc).replace(tzinfo=None)
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AttributeError: 'datetime.date' object has no attribute 'astimezone'
155

This seems to be a problem with Xandikos.

[tobixen]

@jelmer - do you have time to look into the broken test here?

[tobixen]

Sorry for forgetting about this one for so long. Now I can't figure out how to rerun the tests. Hm.

[tobixen]

So the xandikos-problem is with your test code, it is using dates for DTSTART, while datetime probably would be more appropriate. At the other hand, date is a valid type for DTSTART, so perhaps the problem is with xandikos. Hm.

[tobixen]

I have cherry-picked the commit and worked around the xandikos issues. I will raise an issue on the xandikos issue tracker about the breakage. Thanks for the contribution.