Deploy fails with useless error message

[jagthedrummer]

I tried to deploy my extension and it failed with this message:

╭─ error ───────────────────────────────────────────────────────────────────────────────────────────────╮
│                                                                                                       │
│  Version couldn't be created.                                                                         │
│                                                                                                       │
│  theme-app-extension                                                                                  │
│                                                                                                       │
│  Validation errors                                                                                    │
│    • bundle: assets directory should only contain .jpg, .jpeg, .js, .css, .png, .svg, .json, .wasm    │
│      files                                                                                            │
│                                                                                                       │
╰───────────────────────────────────────────────────────────────────────────────────────────────────────╯

It should tell me which file in particular it's not happy about.