Need new Mapbox Tilejson Unit tests

[justb4]

Is your feature request related to a problem? Please describe.
PR #449 had to remove a stale URL that was a public "TileJSON" endpoint for MapBox Vector Tiles in the Dutch SDI PDOK:
https://geodata.nationaalgeoregister.nl/beta/topotiles-viewer/styles/tilejson.json
There is no direct replacement URL as PDOK has changed to OGC API Vector Tiles APIs.

Describe the solution you'd like
Somehow we need an endpoint to test the GHC Probe GeoHealthCheck.plugins.probe.mapbox.TileJSON.

Describe alternatives you've considered
MapTiler has some public endpoints but these require a key. Maybe we can still use.

Additional context
The unit tests were removed by removing these fixtures from tests/data/fixtures.json:

In fixtures.json


Resource
    "PDOK MAPBOX TILEJSON": {
      "owner": "admin",
      "resource_type": "Mapbox:TileJSON",
      "active": true,
      "title": "PDOK BRT+BGT Mapbox TileJSON",
      "url": "https://geodata.nationaalgeoregister.nl/beta/topotiles-viewer/styles/tilejson.json",
      "tags": [
        "pdok",
        "tiling"
      ]
    }
Probe vars
   "PDOK - MAPBOX TILEJSON": {
      "resource": "PDOK MAPBOX TILEJSON",
      "probe_class": "GeoHealthCheck.plugins.probe.mapbox.TileJSON",
      "parameters": {
        "lat_4326": "52",
        "lon_4326": "5"
      }
    }
Check vars

    "PDOK MAPBOX TILEJSON - HTTP - NoError": {
      "probe_vars": "PDOK - MAPBOX TILEJSON",
      "check_class": "GeoHealthCheck.plugins.check.checks.HttpStatusNoError",
      "parameters": {}
    },