Add sidenav test to dependencies controller

What does this MR do?

• Adds a controller test for checking that the side-navigation is expanded when viewing a project's dependency list.
• Changes :have_active_sub_navigation to allow for asserting an active navigation item for both a page-object and response.body

Related Links

• !14425 (closed) - MR that went through a few iterations to come to this result

Screenshots

Does not apply

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
• [-] 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

Closes #12370 (closed)