Add tests for VulnerabilityPresenter

Proposal

VulnerabilityPresenter (ee/app/presenters/vulnerability_presenter.rb) does not have an associated spec file. Write tests for the methods in the presenter. This has actually caused headaches a few times (at least for me) because there's edge cases that don't get checked. These tests can be added for each method or in groups to allow this issue to be iterated through.

Updated status

We have now associated spec file, but we are missing specs for couple of methods.

Implementation plan:

• backend Add specs for #links and #location_text in https://gitlab.com/gitlab-org/gitlab/-/blob/master/ee/spec/presenters/vulnerability_presenter_spec.rb