Add E2E test for trigger matrix

What does this MR do?

This MR adds E2E test for #270957 (closed).

The feature is introduced in: !55348 (merged).

E2E test case gitlab-org/quality/testcases#1732 (closed)

Screenshots (strongly suggested)

Flow::Pipeline.visit_latest_pipeline(pipeline_condition: 'succeeded')

find("[data-qa-selector='child_pipeline'][title*='deploy: [ovh, app]'] [data-qa-selector='expand_pipeline_button']").click
parent_pipeline.click_job('test_vars')

Page::Project::Job::Show.perform do |show|
  expect(show.output).to have_content('ovh')
  expect(show.output).to have_content('app')
end

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
  • I have included a changelog entry.
  • I have not included a changelog entry because _____.
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

End-to-End Test Check-list

• Confirm the test has a testcase: tag linking to an existing test case in the test case project.
• Note if the test is intended to run in specific scenarios. If a scenario is new, add a link to the MR that adds the new scenario.
• Follow the end-to-end tests style guide and best practices.
• Use the appropriate RSpec metadata tag(s).
• Ensure that a created resource is removed after test execution.
• Ensure that no transient bugs are hidden accidentally due to the usage of waits and reloads.
• Verify the tags to ensure it runs on the desired test environments.
• If this MR has a dependency on another MR, such as a GitLab QA MR, specify the order in which the MRs should be merged.
• (If applicable) Create a follow-up issue to document the special setup necessary to run the test: ISSUE_LINK