Data diff: strict checks when no changes expected

[larsyencken]

What

When a PR body says "No data changes expected", make the data diff check strict (i.e. fail with a red cross on any differences).

Why / Why now?

• Today we ignore data diff because it is never green or red
• To make it useful, we should let it fail if no changes are expected
  • This will help it catch cases where we didn't intend to cause changes

[stale]

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