Tests: Use `assertSame()` in `new_admin_email_subject` filter test.

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 [57283].

See #59655.
Built from https://develop.svn.wordpress.org/trunk@57706


git-svn-id: http://core.svn.wordpress.org/trunk@57207 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.5-beta2-57705';
+$wp_version = '6.5-beta2-57706';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.