Incorrectly documented datatype for $request parameter of posts_request filter.

[coffee2code]

The @param docblock for the $request parameter (which represents the "complete SQL query") of the posts_request filter indicates that the parameter has a datatype of array. However, two lines of code earlier it is clearly set as a string.

Patch attached.

[coffee2code]

Patch referenced in ticket.

[DrewAPicture]

In 37848:

Docs: Correct the $request parameter datatype in the hook doc for the posts_request filter.

It's a string, not an array.

Props coffee2code.
Fixes #37142.