🧪 scripts: add missing test for dl_github_archive.py error handling

[ManupaKDU]

🎯 What: The error handling path in scripts/dl_github_archive.py where _hash_check(into) throws an exception within DownloadGitHubTarball.download() lacked test coverage.
📊 Coverage: Added a unit test validating that when the hash check fails, Path.rm_all(into) is invoked exactly once with the target path to clean up the archive, and the exception is appropriately re-raised.
✨ Result: Improved test coverage and reliability for GitHub tarball fetching by validating its error recovery mechanism natively inside the test suite.

Signed-off-by: google-labs-jules[bot] <161369871+google-labs-jules[bot]@users.noreply.github.com>

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PR created automatically by Jules for task 16598151936642151982 started by @manupawickramasinghe

[google-labs-jules]

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