make Autogain work too even if there's no `READSB_RTLSDR_DEVICE` defined #817

Job	Run time
Triggered via Workflow Dispatch?	0s
Deploy with telegraf and healthcheck / Prepare workflow environment	9s
Deploy without telegraf / Prepare workflow environment	5s
Deploy without telegraf / Build (manifest)	2m 47s
Deploy without telegraf / Build nohealthcheck (linux/arm/v7)	2m 18s
Deploy without telegraf / Build nohealthcheck (manifest)	2m 52s
Deploy without telegraf / Build (linux/arm/v7)	2m 0s
Deploy without telegraf / Build nohealthcheck (linux/arm64)	2m 5s
Deploy without telegraf / Build (linux/arm64)	2m 37s
Deploy without telegraf / Build nohealthcheck (linux/amd64)	57s
Deploy without telegraf / Build (linux/amd64)	56s
Deploy with telegraf and healthcheck / Build (manifest)	3m 21s
Deploy with telegraf and healthcheck / Build nohealthcheck (manifest)	3m 7s
Deploy with telegraf and healthcheck / Build nohealthcheck	0s
Deploy with telegraf and healthcheck / Build	0s
Trigger deploy of sdr-enthusiasts/docker-adsb-ultrafeeder	3s
	23m 17s

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