Add unittests for generate_package_indexes_test.py script

[erman-gurses]

Closes #3328
Follow up PR for #3566
Add unittests for generate_package_indexes_test.py script

pytest build_tools/packaging/tests/generate_package_indexes_test.py -vv
=================================================================================== test session starts ===================================================================================
platform linux -- Python 3.12.12, pytest-8.4.2, pluggy-1.6.0 -- /usr/bin/python3
cachedir: .pytest_cache
rootdir: /home/nod/ergurses/TheRock/build_tools
configfile: pyproject.toml
collected 4 items                                                                                                                                                                         

build_tools/packaging/tests/generate_package_indexes_test.py::GeneratePackageIndexesTest::test_generate_index_from_s3_creates_indexes_and_links PASSED                              [ 25%]
build_tools/packaging/tests/generate_package_indexes_test.py::GeneratePackageIndexesTest::test_generate_index_from_s3_respects_max_depth PASSED                                     [ 50%]
build_tools/packaging/tests/generate_package_indexes_test.py::GeneratePackageIndexesTest::test_generate_index_html_skips_dotfiles PASSED                                            [ 75%]
build_tools/packaging/tests/generate_package_indexes_test.py::GeneratePackageIndexesTest::test_generate_top_index_from_s3_lists_subfolders PASSED                                   [100%]

==================================================================================== 4 passed in 0.11s ====================================================================================

[marbre]

@HereThereBeDragons or @araravik-psd please review if the unit tests are meaning full. This won't need a review from me.

[erman-gurses]

@HereThereBeDragons @araravik-psd can you please give a review for that.

[araravik-psd]

Coverage and tests LGTM!