Since some locales may differentiate "Posts" generic post type name (works for both posts, pages, and custom post types) and "Posts" when speaking about blogposts, this change aims to contextualize the use of the "Posts" string in the "Users" admin screen. This change reuses the string used for the "Posts" post type registration, to avoid introducing any new string to translate.
Props audrasjb, jdy68, SergeyBiryukov.
Fixes#54712.
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