Change combined banner over limit check

What does this MR do and why?

In https://gitlab.com/gitlab-org/gitlab/-/issues/433034#note_1695175279 we identified that we should be displaying the combined pre-enforcement banner to namespaces that are >= the user limit, rather than those that are > the user limit.

This MR changes the logic to apply the banner to namespaces that have reached the limit rather than those that are over the limit.

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