[ethernet] fix used pins validation in configuration of RMII pins (#12486)

esphome/components/ethernet/__init__.py

@@ -434,10 +434,13 @@ def _final_validate_rmii_pins(config: ConfigType) -> None:
 
     # Check all used pins against RMII reserved pins
     for pin_list in pins.PIN_SCHEMA_REGISTRY.pins_used.values():
-        for pin_path, _, pin_config in pin_list:
+        for pin_path, pin_device, pin_config in pin_list:
             pin_num = pin_config.get(CONF_NUMBER)
             if pin_num not in rmii_pins:
                 continue
+            # Skip if pin is not directly on ESP, but at some expander (device set to something else than 'None')
+            if pin_device is not None:
+                continue
             # Found a conflict - show helpful error message
             pin_function = rmii_pins[pin_num]
             component_path = ".".join(str(p) for p in pin_path)

tests/components/ethernet/test-lan8720-with-expander.esp32-idf.yaml

@@ -0,0 +1,15 @@
+<<: !include common-lan8720.yaml
+
+sn74hc165:
+  - id: sn74hc165_hub
+    clock_pin: GPIO13
+    data_pin: GPIO14
+    load_pin: GPIO15
+    sr_count: 3
+
+binary_sensor:
+  - platform: gpio
+    pin:
+      sn74hc165: sn74hc165_hub
+      number: 19
+    id: relay_2