Tests: Modernize the `WP_UnitTestCase_Base::assertEqualFields()` method:

* Use `assertSame()` instead of `fail()` to display a proper message in case of failure.
* Add an optional `$message` parameter for consistency with other assertions.

Follow-up to [51478], [51479].

See #53363.
Built from https://develop.svn.wordpress.org/trunk@51480


git-svn-id: http://core.svn.wordpress.org/trunk@51091 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-51479';
+$wp_version = '5.9-alpha-51480';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.