Build/Test Tools: Ensure the `test_php_and_js_shortcode_attribute_regexes_match()` test can run when testing using either the `src` or `build` directory.

Reviewed by desrosj, johnbillion.
Props alexstine, desrosj.
Merges [50501] to the 5.7 branch.
Fixes #51734.
Built from https://develop.svn.wordpress.org/branches/5.7@50509


git-svn-id: http://core.svn.wordpress.org/branches/5.7@50122 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.7-RC3-50508';
+$wp_version = '5.7-RC3-50509';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.