Fix: Icon hourly data rounding issues

[BauerJul]

Description

Fixed an issue with the ICON hourly fix_time function to get rid of some falsly hourly data, cause of rounding issues with the day fraction format ICON used, e.g. got 13:59:59 instead of 14:00:00 and also changed the test file to get exactly that tested.

Checklist

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[codecov]

Codecov Report

Merging #2022 (dc123df) into main (9c91bb3) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #2022   +/-   ##
=======================================
  Coverage   92.78%   92.78%           
=======================================
  Files         236      236           
  Lines       12455    12455           
=======================================
  Hits        11556    11556           
  Misses        899      899           

Impacted Files	Coverage Δ
esmvalcore/cmor/_fixes/icon/icon.py	100.00% <100.00%> (ø)

[schlunma]

Thanks Julian, that looks good to me 🚀