Update code owners for mysqli and mysqlnd [ci-skip]

Author: bukka

.github/CODEOWNERS

@@ -30,7 +30,8 @@
 /ext/json @bukka
 /ext/libxml @nielsdos
 /ext/mbstring @alexdowad @youkidearitai
-/ext/mysqlnd @SakiTakamachi
+/ext/mysqli @bukka @kamil-tekiela
+/ext/mysqlnd @bukka @kamil-tekiela @SakiTakamachi
 /ext/odbc @NattyNarwhal
 /ext/opcache @dstogov
 /ext/openssl @bukka