[E2E] Make change vulnerability status spec deterministic

What does this MR do and why?

Relates to: gitlab-org/quality/quality-engineering/team-tasks#1743 (closed)

This MR changes the random statuses used in the spec to pre-defined ones. Also, adds an example for dismissing vulnerabilities from the report.

Screenshots or screen recordings

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Before	After

How to set up and validate locally

From QA directory:

WEBDRIVER_HEADLESS=false GITLAB_ADMIN_PASSWORD="XXXX" GITLAB_QA_ACCESS_TOKEN=XXXXX GITLAB_PASSWORD="XXXXX" QA_LOG_LEVEL=DEBUG QA_GITLAB_URL=http://192.168.86.46:3000 bundle exec rspec  ./qa/specs/features/ee/browser_ui/10_govern/change_vulnerability_status_spec.rb

MR acceptance checklist

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