Tests: Use `assertSame()` in `_wp_to_kebab_case()` tests.

This ensures that not only the return values match the expected results, but also that their type is the same.

Going forward, stricter type checking by using `assertSame()` should generally be preferred to `assertEquals()` where appropriate, to make the tests more reliable.

Follow-up to [51079], [51198].

See #52482, #52625, #53397.
Built from https://develop.svn.wordpress.org/trunk@51225


git-svn-id: http://core.svn.wordpress.org/trunk@50834 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.8-beta3-51224';
+$wp_version = '5.8-beta3-51225';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.