Use GitHub markdown diff syntax highlighting for assertion failures

It would be nice if assertion failures used syntax highlighting, to make them easier to read, especially when the output is long (e.g. assert.deepEqual).

The following markdown achieves this without changing the layout:

... Skipped lines
  {
    thing: {
+     id: 111,
-     id: 222,
      prop1: 'aaa',
      prop2: 'bbb'
    },
    prop3: 'ccc',
    prop4: 'ddd',
...
          {
+           id: 333,
-           id: 555,
          }
        ],
        prop5: 'eee',
        prop6: 'fff',
        prop7: [

<table>
  <thead>
    <tr>
      <th>Failed Tests</th>
    </tr>
  </thead>
  <tbody>
      <tr>
        <td>
<details>
<summary>❌ Test name</summary>

```diff
... Skipped lines
  {
    thing: {
+     id: 111,
-     id: 222,
      prop1: 'aaa',
      prop2: 'bbb'
    },
    prop3: 'ccc',
    prop4: 'ddd',
...
          {
+           id: 333,
-           id: 555,
          }
        ],
        prop5: 'eee',
        prop6: 'fff',
        prop7: [
```
</details>
        </td>
      </tr>
  </tbody>
</table>

It's a bit clumsy, because of the HTML table, but seems to render okay on GitHub. Can you see any drawbacks?

Locate the code that formats assertion failures and the generated GitHub test summary, then compare its output with the proposed diff-markdown example. The work is done when long assertion failures render with GitHub diff syntax highlighting without changing the existing layout; the payload names no specific files or tests.