fix: replace usage of IOError with OSError

[BoboTiG]

IOError was merged in OSError since Python 3.3 (https://docs.python.org/3/library/exceptions.html#OSError).

[codecov]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 91.88%. Comparing base (5dd30fe) to head (deda7ba).
Report is 33 commits behind head on master.

Files with missing lines	Patch %	Lines
icalevents/icaldownload.py	50.00%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #163   +/-   ##
=======================================
  Coverage   91.88%   91.88%           
=======================================
  Files           4        4           
  Lines         382      382           
  Branches       93       93           
=======================================
  Hits          351      351           
  Misses         14       14           
  Partials       17       17           

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[BoboTiG]

The coverage did not change, weird report 🤔