Render deployment release notes GFM when the release loads

What does this MR do and why?

On the deployment detail page the release notes' GFM was not rendered — renderGFM ran at mount, before the async release query resolved. This watches the release description and runs renderGFM once it is present, so references, syntax highlighting, and other GFM behaviors apply to the notes.

References

• Related to Vue 3 migration: deployment details (show) page (#629158)

Screenshots or screen recordings

Before	After

How to set up and validate locally

The release-notes block only shows on a deployment whose ref is a git tag that has a matching Release, and this change is only visible when that Release's description contains GFM. To create that state:

1. Add a .gitlab-ci.yml that deploys tags to an environment:

   deploy:
     stage: deploy
     script: echo "Deploying $CI_COMMIT_TAG"
     environment:
       name: production
     rules:
       - if: $CI_COMMIT_TAG

2. Go to Deploy → Releases → New release, create a new tag (e.g. v1.0.0), and give the release a description with GFM — an issue reference #1 and a fenced code block. Creating the release makes the tag, which triggers a tag pipeline; the deploy job records a deployment to production.
3. Open the deployment via Operate → Environments → production → the v1.0.0 deployment (/<project>/-/environments/:environment_id/deployments/:iid).
4. In the release notes block under the header, confirm the GFM is processed — #1 renders as an issuable link (hover shows the popover) and the code block is syntax-highlighted. Before this change the notes render as plain, unprocessed HTML.
5. Run the spec:

   yarn jest spec/frontend/deployments/components/deployment_header_spec.js
   VUE_VERSION=3 yarn jest spec/frontend/deployments/components/deployment_header_spec.js

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