Tests: Correct 'meta_query' syntax in test related to WP_User_Query 'who' param.

The test, introduced in [32207], used the incorrect syntax for 'meta_query' -
one fewer level of array-nesting than what `WP_Meta_Query` requires. This
slip uncovered a bug introduced into `WP_User_Query` in [30094], whereby
an incorrectly formatted 'meta_query' parameter would be properly parsed by
`WP_User_Query` when passed alongside `who=authors`.

We need to fix the inconsistent syntax in order to resolve #36724.

See #36724, #32019, #23849, #27026.

git-svn-id: https://develop.svn.wordpress.org/trunk@37359 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/tests/user/query.php

@@ -688,8 +688,10 @@ class Tests_User_Query extends WP_UnitTestCase {
 			'who' => 'authors',
 			'blog_id' => $b,
 			'meta_query' => array(
-				'key' => 'foo',
-				'value' => 'bar',
+				array(
+					'key' => 'foo',
+					'value' => 'bar',
+				)
 			),
 		) );