fix: default calendar needs to support VEVENTs

[st3iny]

To improve the situation in https://github.com/nextcloud/server/issues/45503

Omit calendars that don't support VEVENTs from the default calendar picker.

[st3iny]

/backport to stable4.7

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 1 line in your changes missing coverage. Please review.

Project coverage is 23.59%. Comparing base (de0eef4) to head (99921bc). Report is 5 commits behind head on main.

Files	Patch %	Lines
src/components/AppNavigation/Settings.vue	0.00%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #6041 +/- ## ========================================= Coverage 23.59% 23.59% Complexity 457 457 ========================================= Files 246 246 Lines 11715 11715 Branches 2140 2151 +11 ========================================= Hits 2764 2764 Misses 8637 8637 Partials 314 314 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/6041/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | Coverage Δ | | |---|---|---| | [javascript](https://app.codecov.io/gh/nextcloud/calendar/pull/6041/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.18% <0.00%> (ø)` | | | [php](https://app.codecov.io/gh/nextcloud/calendar/pull/6041/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `58.61% <ø> (ø)` | | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud#carryforward-flags-in-the-pull-request-comment) to find out more.

:umbrella: View full report in Codecov by Sentry.
:loudspeaker: Have feedback on the report? Share it here.