Fix all output_dir in test_trainer.py to use tmp_dir (#35266)

* update codecarbon

* replace directly-specified-test-dirs with tmp_dir

* pass tmp_dir to all get_regression_trainer

* test_trainer.py: Use tmp_dir consistently for all output_dir arguments

* fix some with...as tmp_dir blocks

* reflect the comments to improve test_trainer.py

* refresh .gitignore

Author: nhamanasu