Tooling breaks when "glTF" folder is not present.

The tooling here quietly breaks when the `glTF` folder is not present. Specifically, the tooling issues a warning message to the console during the run, but continues processing anyway. GitHub still places a green checkmark, and it's not obvious anything has gone wrong.

The Playset model added in #116 only includes `glTF-Binary` and does not include a `glTF` folder. But the generated [README.md](https://github.com/KhronosGroup/glTF-Sample-Assets/blob/main/Models/PlaysetLightTest/README.md) for that model fails to list that there are extensions involved:

```
"extensionsUsed": [
"KHR_lights_punctual",
"KHR_materials_emissive_strength"
],
```

At some point I'm sure we talked about the `glTF` folder always being desirable, so that we could have at least one variant that was guaranteed to be present for each sample asset, and so that visitors to this repo would not need special tooling of their own to dismantle our sample assets for better understanding. If this is really the case, we should update the CI here to enforce this. If not, we should update the CI to know how to dismantle a GLB and extract the extensions list and any other needed info from it.

Start with the CI tooling that warns when the glTF folder is absent and the generated README workflow for Models/PlaysetLightTest. Compare the glTF-Binary-only asset and its extensionsUsed metadata, then determine whether CI should enforce a glTF variant or extract metadata from GLB files. Done means CI no longer reports a green check when required processing fails and the generated README lists the relevant extensions.

Written by the indexing model from the issue text.