[Bug-fix] Enable holidays when using global/glocal modeling

[judussoari]

🔬 Background

Fixes #1099
Adding country holidays with m.add_country_holidays() triggers an index error when the input df contains multiple time series (i.e. when glocal/global modeling is used).

🔮 Key changes

Resetting the index of the incoming time series in TimeDataset.make_events_features() resolves the problem.

📋 Review Checklist

• I have performed a self-review of my own code.
• I have commented my code, added docstrings and data types to function definitions.
• I have added pytests to check whether my feature / fix works.

[codecov-commenter]

Codecov Report

Merging #1100 (982bbbc) into main (88c4711) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1100   +/-   ##
=======================================
  Coverage   90.14%   90.14%           
=======================================
  Files          21       21           
  Lines        4798     4799    +1     
=======================================
+ Hits         4325     4326    +1     
  Misses        473      473           

Impacted Files	Coverage Δ
neuralprophet/time_dataset.py	94.64% <100.00%> (+0.01%)	⬆️

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[ourownstory]

LGTM