Test: ensure developers in parent group cannot push without push access

What does this MR do and why?

Adds E2E test as per https://gitlab.com/gitlab-org/gitlab/-/issues/434285 for the scenario described here: https://gitlab.com/gitlab-com/gl-infra/production/-/issues/17213#particular-group-hierarchy-and-permissions-configuration-impacted

This E2E test is a corrective action identified in this discussion: https://gitlab.com/gitlab-com/gl-infra/production/-/issues/17216#note_1681537609

How to set up and validate locally

QA_GITLAB_URL=http://192.168.4.31:3000 GITLAB_QA_PASSWORD_1=<password_for_gitlab-qa-user1> bundle exec rspec qa/specs/features/ee/browser_ui/3_create/repository/restrict_push_protected_branch_spec.rb:102

This has been verified with the problematic MR, see comment: !140765 (comment 1750694960)

Purpose of test

The test setup involves the following elements:

• Sandbox top-level group (All tests use a sandbox group to manage data, this isn't related to the test case)
• parent_group -> sub-group of Sandbox group
• sub_group -> sub-group of parent_group
• user_developer -> member of parent_group (Developer)
• project -> created in parent_group
• protected_branch -> created in project, sub_group is allowed to push

The test then ensures that user_developer cannot push to protected_branch

Screenshots

To explain the scenario i've attached screenshots that the automated test produces.

Parent group

Contains the sub-group and project

Sub group

Contains the developer user (note: i did not add the user, it gets inherited)

Project

Has the developer user and the sub-group as a member

Protected branch:

Sub-group can push and merge, maintainer role added as per https://gitlab.com/gitlab-com/gl-infra/production/-/issues/17213#note_1682717117