[stable4.5] fix: add VTIMEZONE to Appointments

[backportbot-nextcloud]

Backport of #5339

[codecov]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (2940972) 22.08% compared to head (a4b6abf) 22.31%.
Report is 3 commits behind head on stable4.5.

Additional details and impacted files

@@               Coverage Diff               @@
##             stable4.5    #5564      +/-   ##
===============================================
+ Coverage        22.08%   22.31%   +0.22%     
- Complexity         388      406      +18     
===============================================
  Files              240      241       +1     
  Lines            11766    11821      +55     
  Branches          2294     2296       +2     
===============================================
+ Hits              2599     2638      +39     
- Misses            9167     9183      +16     

Flag	Coverage Δ
javascript	13.86% <20.00%> (+<0.01%)	⬆️
php	62.34% <ø> (+0.33%)	⬆️

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Files	Coverage Δ
src/fullcalendar/interaction/eventDrop.js	90.90% <20.00%> (-9.10%)	⬇️

... and 3 files with indirect coverage changes

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