[stable5.1] fix: do not show items from deleted calendars in widget

[backportbot]

Backport of PR #6741

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 14.54%. Comparing base (7557d19) to head (ce87ce7).
Report is 4 commits behind head on stable5.1.

Additional details and impacted files

@@            Coverage Diff             @@
##           stable5.1    #6744   +/-   ##
==========================================
  Coverage      14.54%   14.54%           
==========================================
  Files            210      210           
  Lines           9818     9818           
  Branches        2296     2309   +13     
==========================================
  Hits            1428     1428           
  Misses          8064     8064           
  Partials         326      326           

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javascript	14.54% <ø> (ø)

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