Fixing FutureWarningErrors in Pandas v > 2

[f-allian]

• Further fix to issue Causal surrogate tests are not failing #285 as @jmafoster1 spotted there are additional FutureWarningErrors imposed by newer versions of pandas when running the test suite locally.

[github-actions]

🦙 MegaLinter status: ⚠️ WARNING

Descriptor	Linter	Files	Fixed	Errors	Elapsed time
⚠️ PYTHON	black	29		1	1.24s
✅ PYTHON	pylint	29		0	4.61s

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.62%. Comparing base (f77a45c) to head (5af464f).
Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #288   +/-   ##
=======================================
  Coverage   95.61%   95.62%           
=======================================
  Files          22       22           
  Lines        1529     1530    +1     
=======================================
+ Hits         1462     1463    +1     
  Misses         67       67           

Files	Coverage Δ
causal_testing/testing/estimators.py	89.27% <100.00%> (+0.04%)	⬆️

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[f-allian]

Also closes issue #285