Add [DEPREACTED] label

What does this MR do and why?

In previous MR, we updated the API documentation to add [DEPRECATED] labels. We forgot to add it to the code description too.

This MR, adds the missing [DEPRECATED] label to also to the deprecated internal API code description

References

Please include cross links to any resources that are relevant to this MR. This will give reviewers and future readers helpful context to give an efficient review of the changes introduced.

• https://gitlab.com/gitlab-org/gitlab/-/issues/473624+

• Update gitlab_subscriptions.md doc (!173860 - merged)

MR acceptance checklist

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