References to `$wpdb` should use `@global` not `@uses`

[DrewAPicture]

In [30105] we removed most of the standalone @uses tags from core documentation where they referred to functions used by functions. The attached patch begins the effort to convert other erroneous uses of the @uses tag, in this case when documenting that the $wpdb global is leveraged.

[DrewAPicture]

In 30122:

Correct references of @uses $wpdb in core documentation to use @global.

See #30191, [30105].
Fixes #30217.