Support Solidus v4

[waiting-for-dev]

• Update CI configuration

• Fetch Solidus from new main branch and don't resolve SF v4

• Use new way to load factories

• Fix spec

• Use new way to release extensions

[waiting-for-dev]

CI failure looks unrelated

[waiting-for-dev]

There's a wrong ref in the fouth commit description, but +1

Thanks, fixed!