Coding Standards: Use `__DIR__` instead of `ABSPATH` in `wp-db.php`.

If the file is included directly outside of WordPress core, `ABSPATH` may not be defined.

Follow-up to [53749], [53750], [53755].

See #56268, #55647.
Built from https://develop.svn.wordpress.org/trunk@53756


git-svn-id: http://core.svn.wordpress.org/trunk@53315 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-53755';
+$wp_version = '6.1-alpha-53756';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.

wp-includes/wp-db.php

@@ -14,4 +14,4 @@ if ( function_exists( '_deprecated_file' ) ) {
 }
 
 /** wpdb class */
-require_once ABSPATH . 'wp-includes/class-wpdb.php';
+require_once __DIR__ . '/class-wpdb.php';