Fix storagetransfer transferoptions perm diff

[modular-magician]

Fix #11744

There was a issue with transferOptions always returning from API when using posix,
I think This fix added, probably.
but it had too large effect to other cases.
So I fixed to use only posix case.

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storagetransfer: fixed perm diff on transfer_options for `google_storage_transfer_job`

Derived from GoogleCloudPlatform/magic-modules#6063

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