italy_yaml fix loading datetimes

[prandla]

parse_datetime is already called in make_group, so we mustn't use it with main_group options. (otherwise we will call parse_datetime or make_timedelta twice, which is incorrect. this caused me a very infuriating debug session because i thought my fix for #1565 was somehow buggy.)

[codecov]

Codecov Report

❌ Patch coverage is 0% with 5 lines in your changes missing coverage. Please review.
✅ Project coverage is 56.71%. Comparing base (c76c40d) to head (10cb28c).
✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
cmscontrib/loaders/italy_yaml.py	0.00%	5 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1724      +/-   ##
==========================================
- Coverage   56.71%   56.71%   -0.01%     
==========================================
  Files         344      344              
  Lines       28307    28307              
==========================================
- Hits        16055    16054       -1     
- Misses      12252    12253       +1     

Flag	Coverage Δ
functionaltests	0.00% <0.00%> (ø)
unittests	56.71% <0.00%> (-0.01%)	⬇️

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