MAINTAINERS.yml: add net/mii.h header to ethernet area

add include/zephyr/net/mii.h header to ethernet area.

Signed-off-by: Fin Maaß <f.maass@vogl-electronic.com>

Author: maass-hamburg

MAINTAINERS.yml

@@ -1460,6 +1460,7 @@ Release Notes:
     - tests/drivers/ethernet/
     - include/zephyr/drivers/ethernet/
     - include/zephyr/net/phy.h
+    - include/zephyr/net/mii.h
     - include/zephyr/net/ethernet.h
   labels:
     - "area: Ethernet"