Dedent task docstrings used as doc_md

[yuseok89]

closes: #66477

A @task function's docstring used as doc_md keeps the leading indentation from the nested function, so it renders as an indented code block instead of Markdown. This applies inspect.cleandoc to fix it.

Picks up the approved-then-stale #68500 with the review feedback applied.

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  • Opus 4.8

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