fix(diff): last test generation

[nicojs]

Fix a bug in the diffing algorithm where, running in --incremental mode, the test file would always be marked as 'changed' when it contained tests generated using a function, which was the last in the file.

For example:

import { add } from "../add.js";

test.each`
  x    | y    | expected
  ${1} | ${1} | ${2}
  ${1} | ${2} | ${3}
  ${2} | ${2} | ${4}
`("add($x, $y) = $expected", ({ x, y, expected }) => {
  expect(add(x, y)).toBe(expected);
});

Closes #3909