This very simple page allows you to publish an assetlinks.json file at the location [domain.com]/.well-known/assetlinks.json, for the purpose of testing.
To make sure this works, you must:
[yourgithubusername].github.io
for the repository name.assetlinks.json
file:
---
layout: none
permalink: .well-known/assetlinks.json
---
Yes, this is invalid JSON, but the actual served content will be fine.