[core] Enable ruff SLOT (flake8-slots) lint family (#16647)

pyproject.toml

@@ -125,6 +125,7 @@ select = [
   "PL",   # pylint
   "Q",    # flake8-quotes
   "SIM",  # flake8-simplify
+  "SLOT", # flake8-slots
   "RET",  # flake8-ret
   "T10",  # flake8-debugger
   "UP",   # pyupgrade

tests/unit_tests/test_yaml_util.py

@@ -907,7 +907,7 @@ def test_format_path_current_obj_without_location_falls_back_to_key():
     """An ESPHomeDataBase current_obj with no esp_range falls back to the key's location."""
 
     class _NoRange(ESPHomeDataBase, str):
-        pass
+        __slots__ = ()
 
     obj = _NoRange.__new__(_NoRange, "value")
     str.__init__(obj)