This reverts merge request !143297

In the sign in pages users access the application either by:
- A tabulated multiform
- A single standard form

We combine HAML partials so the structure matches the same logic:
- Multiform sign in with tabs
- Single standard sign in

In addition, we cleanup HAML variables and QA selectors.

Quarantine Package RubyGems Repository publishes a Ruby gem

Quarantine Create new merge request from the event notification after a push via the API creates a merge request

Quarantine Create Protected branch support when developers and maintainers are not allowed to push to a protected branch user without push rights fails to push

Use selector in end-to-end tests

Fixed a bug where reviews were not mapped to users.

And updated GitHub Import E2E to not use
`single_endpoint_issue_events_import` import option as the option
is no longer available when `github_import_extended_events` FF is
enabled.

Changelog: fixed

This reverts merge request !142554

Changelog: fixed
EE: true

Fixes https://gitlab.com/gitlab-org/gitlab/-/issues/439683

Changelog: changed