All day event timezone fix

[mshish]

Attempts to fix #85
Two changes:

1. Bring in fix from Fix caldav TZ interpretation of all day events home-assistant/core#48642 which doesn't make much of a difference here (branch doesn't appear to get hit with all day events).
2. Fix the timezone shift for all day events. I'm not sure this is in the right place since it appears o365 is returning the event as if it were on GMT (but it's not). This may only work if the all day event was actually in the local timezone.

[sourcery-ai]

Sourcery Code Quality Report

❌  Merging this PR will decrease code quality in the affected files by 0.94%.

Quality metrics	Before	After	Change
Complexity	2.28 ⭐	2.49 ⭐	0.21 👎
Method Length	53.00 ⭐	55.13 ⭐	2.13 👎
Working memory	9.40 🙂	9.53 🙂	0.13 👎
Quality	71.62% 🙂	70.68% 🙂	-0.94% 👎

Other metrics	Before	After	Change
Lines	304	312	8

Changed files	Quality Before	Quality After	Quality Change
custom_components/o365/calendar.py	71.62% 🙂	70.68% 🙂	-0.94% 👎

Here are some functions in these files that still need a tune-up:

File	Function	Complexity	Length	Working Memory	Quality	Recommendation
custom_components/o365/calendar.py	setup_platform	8 ⭐	160 😞	12 😞	50.41% 🙂	Try splitting into smaller methods. Extract out complex expressions
custom_components/o365/calendar.py	CalendarServices.respond_calendar_event	5 ⭐	136 😞	11 😞	57.61% 🙂	Try splitting into smaller methods. Extract out complex expressions
custom_components/o365/calendar.py	O365CalendarData.async_update	1 ⭐	110 🙂	15 😞	58.79% 🙂	Extract out complex expressions
custom_components/o365/calendar.py	O365CalendarData.async_get_events	4 ⭐	114 🙂	10 😞	63.16% 🙂	Extract out complex expressions
custom_components/o365/calendar.py	O365CalendarEventDevice.async_update	1 ⭐	98 🙂	12 😞	64.65% 🙂	Extract out complex expressions

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• ⛔ very poor

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[franc6]

If O365 uses RFC 5545, then it can be assumed that all-day events are always in the local time zone.

[mshish]

Do I need to address the Sourcery issues to get this accepted?