[MNT] `mypy` fixes

[satvshr]

Once #1637 is merged:

Fixes required due to Mypy version upgrade (v1.13.0 to v1.19.1)

These files were functional under older Mypy versions but now report errors.

[ ] examples._external_or_deprecated.upload_amlb_flows_and_runs
[ ] examples._external_or_deprecated.run_setup_tutorial
[ ] examples._external_or_deprecated.flows_and_runs_tutorial
[ ] examples._external_or_deprecated.flow_id_tutorial
[ ] examples._external_or_deprecated.fetch_runtimes_tutorial
[ ] examples._external_or_deprecated.benchmark_with_optunahub
[ ] examples._external_or_deprecated.2018_neurips_perrone_example
[ ] examples._external_or_deprecated.2018_ida_strang_example
[ ] examples._external_or_deprecated.2015_neurips_feurer_example
[ ] examples.Basics.simple_tasks_tutorial
[ ] examples.Basics.simple_suites_tutorial
[ ] examples.Basics.simple_flows_and_runs_tutorial
[ ] examples.Basics.simple_datasets_tutorial
[ ] examples.Advanced.task_manual_iteration_tutorial
[ ] examples.Advanced.study_tutorial
[ ] examples.Advanced.fetch_evaluations_tutorial
[ ] examples.Advanced.datasets_tutorial
[ ] examples.Advanced.create_upload_tutorial

Fixes required for the tests directory

These files need to be addressed after removing the global skip on the tests directory.

[ ] tests.conftest
[ ] tests.test_datasets.test_dataset
[ ] tests.test_datasets.test_dataset_functions
[ ] tests.test_evaluations.test_evaluation_functions
[ ] tests.test_evaluations.test_evaluations_example
[ ] tests.test_extensions.test_functions
[ ] tests.test_flows.dummy_learn.dummy_forest
[ ] tests.test_flows.test_flow
[ ] tests.test_flows.test_flow_functions
[ ] tests.test_openml.test_api_calls
[ ] tests.test_openml.test_cli
[ ] tests.test_openml.test_config
[ ] tests.test_openml.test_openml
[ ] tests.test_runs.test_run
[ ] tests.test_runs.test_run_functions
[ ] tests.test_runs.test_trace
[ ] tests.test_setups.test_setup_functions
[ ] tests.test_study.test_study_functions
[ ] tests.test_tasks.test_classification_task
[ ] tests.test_tasks.test_clustering_task
[ ] tests.test_tasks.test_learning_curve_task
[ ] tests.test_tasks.test_regression_task
[ ] tests.test_tasks.test_split
[ ] tests.test_tasks.test_supervised_task
[ ] tests.test_tasks.test_task
[ ] tests.test_tasks.test_task_functions
[ ] tests.test_tasks.test_task_methods
[ ] tests.test_utils.test_utils