BUGFIX: Improve coverage

[ThibTrip]

Improved bad coverage due to using pytest multiple times and then calling codecov instead of just a single pytest and then codecov.

[codecov-io]

Codecov Report

Merging #9 into master will increase coverage by 12.53%.
The diff coverage is 96.29%.

@@             Coverage Diff             @@
##           master       #9       +/-   ##
===========================================
+ Coverage   76.99%   89.53%   +12.53%     
===========================================
  Files          12       12               
  Lines         526      535        +9     
===========================================
+ Hits          405      479       +74     
+ Misses        121       56       -65     

Impacted Files	Coverage Δ
pangres/tests/conftest.py	96.96% <93.75%> (-3.04%)	⬇️
pangres/examples.py	100.00% <100.00%> (ø)
pangres/tests/test_chunsize.py	100.00% <100.00%> (ø)
pangres/tests/test_pandas_special_engine.py	100.00% <100.00%> (ø)
pangres/tests/test_upsert.py	100.00% <100.00%> (+11.11%)	⬆️
pangres/tests/test_upsert_speed.py	74.19% <100.00%> (ø)
pangres/helpers.py	89.83% <0.00%> (+7.34%)	⬆️
pangres/tests/test_index.py	96.55% <0.00%> (+13.79%)	⬆️
pangres/utils.py	80.00% <0.00%> (+57.14%)	⬆️
... and 1 more

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