Update Data Classification Policy Links on website

What does this MR do?

Fixing Broken Link - haiku by @greg

Hyperlink is broke.

Docs need merge request to fix.

Fixes broken link.

Why is this change being made?

• https://about.gitlab.com/handbook/engineering/security/data-classification-policy.html 😩
• https://about.gitlab.com/handbook/engineering/security/data-classification-standard.html 😀

@JohnathanHunt @ralfaro @jburrows001 @JamesRLopes @axil If you all approve, I just need someone to merge it. 🙏

See also

gitlab-org/gitlab!42012 (merged)

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per [say-why-not-just-what][transparency]
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in [#mr-buddies][mr-buddies-slack].
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files.