15.9 release post: Fix tier badge for Release self-approval setting for protected environments

Why is this change being made?

The tier badge for self-approval settings for protected environments shows as Premium only. This seems to be caused by the issue not having the Ultimate label. gitlab-org/gitlab#381418 (closed) Item for the release retrospective.

This MR updates the tier badges in the release post item.

Note: This MR is based on the release-15-9 branch and can be merged, it has set the correct target branch.

Author Checklist

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