Update Govern stage verification steps URL in bot messages

What does this MR do and why?

Updates the URL the bot messages link to for verification:

• Current and broken: https://about.gitlab.com/handbook/engineering/development/sec/govern/planning/#verification
• Updated and working: https://about.gitlab.com/handbook/engineering/development/sec/govern/sp-ti-planning.html#verification

Example of a broken link: gitlab-org/gitlab#381714 (comment 1252122704)

Action items

• If adding environment variables for reactive processors, update config/triage-web.yaml and .gitlab/ci/triage-web.yml
• (If applicable) Add documentation to the handbook pages for Triage Operations =>
• (If applicable) Identify the affected groups and how to communicate to them:
  • /cc @person_or_group =>
  • Relevant Slack channels =>
  • Engineering week-in-review