[ci skip] Revert2: Add Hamada-san to CODEOWNERS for mbstring (php#14744)

This reverts commit 1b47fd0.
I (@youkidearitai) join to CODEOWNERS for mbstring.

Author: youkidearitai

.github/CODEOWNERS

@@ -22,7 +22,7 @@
 /ext/intl @devnexen
 /ext/json @bukka
 /ext/libxml @nielsdos
-/ext/mbstring @alexdowad
+/ext/mbstring @alexdowad @youkidearitai
 /ext/mysqlnd @SakiTakamachi
 /ext/odbc @NattyNarwhal
 /ext/opcache @dstogov @iluuu1994