Handbook: TR US benefits, remove space from 2023 costs header

Why is this change being made?

Fix a rendering glitch on https://about.gitlab.com/handbook/total-rewards/benefits/general-and-entity-benefits/inc-benefits-us/

The 2023 rates had a leading space before the sub-header for 2023, resulting in a failure to be rendered as a proper header, as with 2022

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