Adding wait for vulnerability to show up in fix vuln workflow spec

What does this MR do and why?

Tries to address: #387839 (closed).

1. This failure is not reproducible when run locally against staging and canary environments.
2. By looking at the logs, it seems like it takes some time for the vulnerability report to load in these environments even after the pipeline on the default branch is finished. We wait for the pipeline to complete here but when I navigated to the project vulnerability report from failed spec logs, it seems that the report is loaded a few moments after the expectation fails. This MR accounts for that possibility.

How to set up and validate locally

Test against canary:

WEBDRIVER_HEADLESS=false GITLAB_USERNAME=XXX GITLAB_PASSWORD="XXXX" QA_COOKIES="gitlab_canary=true" GITLAB_QA_USER_AGENT="XXX" QA_DEBUG=true QA_GITLAB_URL=https://gitlab.com bundle exec rspec ./qa/specs/features/ee/browser_ui/10_govern/fix_vulnerability_workflow_spec.rb

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.