Adapt to js_exec changes in zig-js-runtime

[krichprollsch]

the wpt tests are failing b/c there is a JS error displayed on stderr that wasn't here before.

In this PR:

$ zig build wpt -- --json tests/wpt/dom/parts/basic-dom-part-objects.tentative.html
:566: Uncaught TypeError: Cannot read properties of undefined (reading 'cloneNode')
[
  {
    "pass": false,
    "crash": false,
    "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
    "cases": [
      {
        "pass": false,
        "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
        "message": "JSExec"
      }
    ]
  }
]

In main:

$ zig build wpt -- --json tests/wpt/dom/parts/basic-dom-part-objects.tentative.html
[
  {
    "pass": false,
    "crash": false,
    "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
    "cases": [
      {
        "pass": false,
        "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
        "message": "TypeError: Cannot read properties of undefined (reading 'cloneNode')\n    at <anonymous>:15:42\n    at Array.forEach (<anonymous>)\n    at <anonymous>:7:14"
      }
    ]
  }
]

[krichprollsch]

Fixed

$ zig build wpt -- --safe --json tests/wpt/dom/parts/basic-dom-part-objects.tentative.html
[
  {
    "pass": false,
    "crash": false,
    "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
    "cases": [
      {
        "pass": false,
        "name": "tests/wpt/dom/parts/basic-dom-part-objects.tentative.html",
        "message": "TypeError: Cannot read properties of undefined (reading 'cloneNode')\n    at <anonymous>:15:42\n    at Array.forEach (<anonymous>)\n    at <anonymous>:7:14"
      }
    ]
  }
]