Update data-tests.md. Solving double negative.

[ialdg]

Hi.
Since the tests looks for negative amount records, why not say so instead of using a double negative, which is not the easiest to read and involves longer code? Regards.
IL.

What are you changing in this pull request and why?

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Adding or removing pages (delete if not applicable):

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• Run link testing locally with npm run build to update the links that point to deleted pages

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[matthewshaver]

Thank you @ialdg Made another edit to add clarity to the whole section and will merge this.