Change trigger platform key to trigger (#124357)

* fix

* Fix

* Fix

* Update homeassistant/helpers/config_validation.py

Co-authored-by: Erik Montnemery <erik@montnemery.com>

* Fix

* Fix

* Fix

* Fix

* Add more tests

* Fix

* Fix tests

* Add tests

* Let's see what the CI does

* It fails on the code that tested the thing ofc

* It fails on the code that tested the thing ofc

* Revert test thingy

* Now the test works again, lovely

* Another one

* Fix websocket thingy

* Only copy when needed

* Improve comment

* Remove test

* Fix docstring

* I think this now also work since this transforms trigger to platform

* Add comment

* Update homeassistant/helpers/config_validation.py

Co-authored-by: Erik Montnemery <erik@montnemery.com>

* Update homeassistant/helpers/config_validation.py

Co-authored-by: Erik Montnemery <erik@montnemery.com>

* Update homeassistant/helpers/config_validation.py

Co-authored-by: Erik Montnemery <erik@montnemery.com>

* Check for mapping

* Add test

* Update homeassistant/helpers/config_validation.py

Co-authored-by: Erik Montnemery <erik@montnemery.com>

* Update test to also test for trigger keys

---------

Co-authored-by: Erik Montnemery <erik@montnemery.com>

tests/helpers/test_selector.py

@@ -1,6 +1,7 @@
 """Test selectors."""
 
 from enum import Enum
+from typing import Any
 
 import pytest
 import voluptuous as vol
@@ -1107,6 +1108,13 @@ def test_condition_selector_schema(
         (
             {},
             (
+                [
+                    {
+                        "platform": "numeric_state",
+                        "entity_id": ["sensor.temperature"],
+                        "below": 20,
+                    }
+                ],
                 [
                     {
                         "platform": "numeric_state",
@@ -1122,7 +1130,24 @@ def test_condition_selector_schema(
 )
 def test_trigger_selector_schema(schema, valid_selections, invalid_selections) -> None:
     """Test trigger sequence selector."""
-    _test_selector("trigger", schema, valid_selections, invalid_selections)
+
+    def _custom_trigger_serializer(
+        triggers: list[dict[str, Any]],
+    ) -> list[dict[str, Any]]:
+        res = []
+        for trigger in triggers:
+            if "trigger" in trigger:
+                trigger["platform"] = trigger.pop("trigger")
+            res.append(trigger)
+        return res
+
+    _test_selector(
+        "trigger",
+        schema,
+        valid_selections,
+        invalid_selections,
+        _custom_trigger_serializer,
+    )
 
 
 @pytest.mark.parametrize(