Build/Test: Change default GitHub branch to trunk

See: https://make.wordpress.org/core/2021/11/10/default-git-branch-for-wordpress-wordpress-develop/
See: https://make.wordpress.org/core/2020/06/18/proposal-update-all-git-repositories-to-use-main-instead-of-master/

Fixes #54399


Built from https://develop.svn.wordpress.org/trunk@52130


git-svn-id: http:https://core.svn.wordpress.org/trunk@51722 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.9-alpha-52129';
+$wp_version = '5.9-alpha-52130';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.