Docs: Add missing `@since` and properly mark the optional `$type` parameter as...

Docs: Add missing `@since` and properly mark the optional `$type` parameter as such in the DocBlock for the deprecated `get_others_unpublished_posts()` function.

Introduced in [5707].

See #32246.

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git-svn-id: https://core.svn.wordpress.org/trunk@36036 1a063a9b-81f0-0310-95a4-ce76da25c4cd