CODEOWNERS: add @fuz for libc/string

Approved by:	markj (mentor)
Differential Revision:	https://reviews.freebsd.org/D54664

.github/CODEOWNERS

@@ -51,6 +51,8 @@
 /crypto/openssl/	@juikim
 /etc/mail	@gshapiro
 /etc/sendmail	@gshapiro
+/lib/libc/string/	@fuz
+/lib/libc/*/string/	@fuz
 /lib/libc/sys/kevent.c	@jmgurney
 /lib/libefivar/	@bsdimp
 /lib/libfetch	@dag-erling