Update deprecation milestone for job token setting

What does this MR do and why?

As per the related MR, we need to update deprecation milestone for the job token setting in the UI and API docs as well.

While looking at the UI text, I realized we also needed to clarify the message, as the setting names changed in 16.3 but we never updated the deprecation warning to match.

• Related to !146947 (merged)
• Related to https://gitlab.com/gitlab-com/Product/-/issues/13137#note_1806437438

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