fix pandas future warnings

[solegalli]

closes #778

[codecov]

Codecov Report

Attention: Patch coverage is 87.50000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 97.85%. Comparing base (178464f) to head (3d888d9).
Report is 1 commits behind head on main.

Files	Patch %	Lines
..._engine/variable_handling/_variable_type_checks.py	0.00%	0 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #795      +/-   ##
==========================================
- Coverage   97.89%   97.85%   -0.05%     
==========================================
  Files         107      107              
  Lines        4284     4290       +6     
  Branches      855      857       +2     
==========================================
+ Hits         4194     4198       +4     
- Misses         54       55       +1     
- Partials       36       37       +1     

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