Fix file stream

[gwyneplaine]

Don't manually pipe your stream like an idiot.
Use stream.pipeline instead.

Node 15 has a native promisified version of this function, but since we're not on 15, doing it manually.

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🦋 Changeset detected

Latest commit: 241fd6a

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@keystone-next/test-utils-legacy	Patch

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[timleslie]

Nice fix!