fix(sdk): fix incorrect sub-DAG output type when using dsl.Collected

[connor-mccarthy]

Description of your changes:
Non-functional fix. The return type of a dsl.ParallelFor group that has a dsl.Collected on it had an incorrect return type. The pipeline would still run, but the output was technically incorrect.

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[connor-mccarthy]

/assign @chensun

[chensun]

/lgtm
/approve

Thanks!

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