`GatewayRunner` never had a `get_adapter` method, so every gateway `/save`
(Telegram, Discord, ...) rendered the file and then failed with
"'GatewayRunner' object has no attribute 'get_adapter'". Resolve the adapter
through `_adapter_for_source`, the profile-aware lookup the rest of the runner
uses, so multiplex secondaries deliver through their own bot rather than a
missing key on the default map.
Co-authored-by: pierrenode <298902573+pierrenode@users.noreply.github.com>
Co-authored-by: KoNit-K <124019182+KoNit-K@users.noreply.github.com>
Co-authored-by: Baophan00 <109447498+Baophan00@users.noreply.github.com>
teknium1