Can't change pack's logLevel since 0.17

[jcare44]

Hey!

I've been updating old projects lately, and I can't seem to be able to change the logLevel of pack tasks like I used to.
Prior to 0.17, I could define a setting like (pack / logLevel) := Level.Warn, and it would mute all the out.log.info() done by pack. But from 0.17 onward, it doesn't seem to do anything.
The only way I found to have it working again was to do something like ThisBuild / logLevel := Level.Warn, but that would impact every task & config, which I don't want.

As for the cause of this change, I would guess that it comes from #324 and its use of Def.derive().

Is there a new way to still change the logLevel today that I haven't found?
If not, sadly, I don't know enough of sbt's inner-workings to fix this myself. Does someone have an idea?

Thanks!