upgrade pandas 1.5 -> 2.0

[emanuel-schmid]

append and iteritems are no longer methods of pandas DataFrame.

Failing Tests:

• climada.engine.unsequa.test.test_unsequa.TestCalcCostBenefit.test_calc_sensitivity_pass
• climada.engine.unsequa.test.test_unsequa.TestCalcCostBenefit.test_calc_uncertainty_pass
• climada.engine.unsequa.test.test_unsequa.TestCalcCostBenefit.test_calc_uncertainty_pool_pass
• climada.engine.unsequa.test.test_unsequa.TestCalcImpact.test_calc_sensitivity_morris_pass
• climada.engine.unsequa.test.test_unsequa.TestCalcImpact.test_calc_sensitivity_pass
• climada.engine.unsequa.test.test_unsequa.TestOutput.test_plot_unc_imp
• climada.engine.unsequa.test.test_unsequa.TestOutput.test_save_load_pass
• climada.util.test.test_lines_polys_handler.TestGeomImpactCalcs.test_calc_geom_impact_mixed
• climada.util.test.test_lines_polys_handler.TestGeomImpactCalcs.test_impact_pnt_agg

[chahank]

iteritems must apparently be replaced with items and append with pd.concat.

[ThomasRoosli]

Another possible stopper for the update is apparently the pandas.Series.resample()/pandas.DataFrame.resample()/pandas.Grouper methodologies that no longer accepts the deprecated parameter base.
This could be another reason for some of the failing tests.

[chahank]

All the unsequa tests are now passing after merging of PR #763 .

[chahank]

For the other two tests #777 should have solved this.