Fix typing for entity_platform.async_register_entity_service

[KapJI]

Proposed change

I think this should accept vol.Marker because:

1. If this argument is a dict it's passed to config_validation.make_entity_service_schema where it's unwrapped to vol.Schema.
2. Similar entity_component.async_register_entity_service accepts vol.Marker.

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[frenck]

Thanks, @KapJI 👍

../Frenck