CODEOWNERS: update for ndossche's rename (#5061)

c.f. php/php-src@2e0ab27

Author: DanielEScherzer

CODEOWNERS

@@ -8,9 +8,9 @@
 # For more information, see the GitHub CODEOWNERS documentation:
 # https://docs.github.com/en/repositories/managing-your-repositorys-settings-and-features/customizing-your-repository/about-code-owners
 
-/reference/dom @nielsdos
+/reference/dom @ndossche
 /reference/hash @TimWolla
-/reference/libxml @nielsdos
+/reference/libxml @ndossche
 /reference/mysqli @kamil-tekiela
 /reference/mysqlnd @kamil-tekiela
 /reference/pdo @kamil-tekiela