[stable4.7] fix: don't apply default calendar on Nextcloud < 29

[backportbot[bot]]

Backport of PR #5980

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes are missing coverage. Please review.

Project coverage is 15.49%. Comparing base (77e8ff7) to head (29d15ca). Report is 1 commits behind head on stable4.7.

Files	Patch %	Lines
src/store/calendarObjects.js	0.00%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## stable4.7 #5981 +/- ## ============================================= - Coverage 15.49% 15.49% -0.01% ============================================= Files 206 206 Lines 9255 9257 +2 Branches 1930 1931 +1 ============================================= Hits 1434 1434 - Misses 7821 7823 +2 ``` | [Flag](https://app.codecov.io/gh/nextcloud/calendar/pull/5981/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/5981/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=nextcloud) | `15.49% <0.00%> (-0.01%)` | :arrow_down: | 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.

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