Improve testing on GH Pages

[myasnikovdaniil]

Some issues was found on production deploy in GitHub Pages that can't be caught on Netlify preview.

1. Redirect from v1 pages to v1.0/v1.2 didn't work. Fixed via fix: update /docs/v1/ redirect to latest v1.2 #492
2. Openapi download not run on GH, probably config issue. Fixed via fix(ci): add OpenAPI spec download to GitHub Pages build #494

So same situations need to be addressed with some tests before it hits production deploy.