Tests: Resolve `WP_Query` test failures on MariaDB due to indeterminate sort order.

[54768] added a few tests to verify that caching within `WP_Query` is bypassed when the `SELECT` clause has been modified via a filter, to avoid cache key collisions and the returning of incomplete or unexpected results.

However, creating several posts with the same date/time fields can result in inconsistent sort ordering between MySQL and MariaDB, as each engine refines the order further using a different index.

This commit aims to stabilize the tests by using `assertEqualSets()` instead of `assertEquals()`, since testing the order is out of their scope. Includes removing `array_unshift()` and `array_reverse()` calls as no longer needed.

This resolves a few test failures on MariaDB along the lines of:
{{{
Tests_Query_FieldsClause::test_should_limit_fields_to_id_and_parent_subset
Posts property for first query is not of expected form.
Failed asserting that two arrays are equal.
--- Expected
+++ Actual
@@ @@
 Array (
     0 => stdClass Object (
-        'ID' => 36019
+        'ID' => 36015
         'post_parent' => 0
     )
     1 => stdClass Object (
-        'ID' => 36018
+        'ID' => 36016
         'post_parent' => 0
     )
     2 => stdClass Object (...)
     3 => stdClass Object (
-        'ID' => 36016
+        'ID' => 36018
         'post_parent' => 0
     )
     4 => stdClass Object (
-        'ID' => 36015
+        'ID' => 36019
         'post_parent' => 0
     )
 )

/tmp/wp-test-runner/tests/phpunit/tests/query/fieldsClause.php:67
/tmp/wp-test-runner/phpunit-5.7.phar:598
}}}

Follow-up to [54768].

Props peterwilsoncc, SergeyBiryukov.
Merges [54829] to the 6.1 branch.
Fixes #57012.
Built from https://develop.svn.wordpress.org/branches/6.1@54830


git-svn-id: http://core.svn.wordpress.org/branches/6.1@54382 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1.1-RC1-54828';
+$wp_version = '6.1.1-RC1-54830';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.