[6/7] feat(test): report `PrepareWorkingDirectoryError` reason

[arxanas]

Stack:

• https://github.com/arxanas/git-branchless/pull/1353
• https://github.com/arxanas/git-branchless/pull/1354
• https://github.com/arxanas/git-branchless/pull/1355
• https://github.com/arxanas/git-branchless/pull/1356
• https://github.com/arxanas/git-branchless/pull/1202
• https://github.com/arxanas/git-branchless/pull/1357
• https://github.com/arxanas/git-branchless/pull/1358

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feat(test): report PrepareWorkingDirectoryError reason