Updates the deprecation documentation URL

What does this MR do and why?

Describe in detail what your merge request does and why.

We recently updated the release post documentation which included updates to anchor tags for deprecated features instructions. This MR updates that URL in the template used to build the deprecations file.

How to set up and validate locally

Numbered steps to set up and validate the change are strongly suggested.

1. validate that the link goes to the correct handbook location and anchor
2. (optional) run the lib/tasks/gitlab/docs/compile_deprecations.rake task to rebuild the deprecations file. It should include the same properly formatted URL as well.

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.