[rtttl] add new codeowner (#14440)

CODEOWNERS

@@ -412,7 +412,7 @@ esphome/components/rp2040_pio_led_strip/* @Papa-DMan
 esphome/components/rp2040_pwm/* @jesserockz
 esphome/components/rpi_dpi_rgb/* @clydebarrow
 esphome/components/rtl87xx/* @kuba2k2
-esphome/components/rtttl/* @glmnet
+esphome/components/rtttl/* @glmnet @ximex
 esphome/components/runtime_image/* @clydebarrow @guillempages @kahrendt
 esphome/components/runtime_stats/* @bdraco
 esphome/components/rx8130/* @beormund