HTML API: Improve skipped test reporting with unsupported exception.

The `html5lib-tests` suite skips a number of tests due to unsupported markup. At the moment, these tests all report "Test includes unsupported markup." This patch calls the `get_unsupported_exception()` method in these skipped cases to improve the messages reported to PHPUnit so they're more informative: e.g. "Unsupported markup: Foster parenting is not supported."

Developed in WordPress/wordpress-develop#7285
Discussed in https://core.trac.wordpress.org/ticket/61646

Follow-up to [58714].

Props dmsnell, jonsurrell.
See #61646.

Built from https://develop.svn.wordpress.org/trunk@58971


git-svn-id: http://core.svn.wordpress.org/trunk@58367 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.7-alpha-58970';
+$wp_version = '6.7-alpha-58971';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.