Use correct rust log level in dockerfiles

[loneil]

From issue #2498

It looks like warning is not a valid Rust log level string https://docs.rs/log/latest/log/enum.Level.html
From what I've seen in traction (which deploys using the dockerfile here), this means logs default to INFO level here even though dockerfile is trying to have it at the warn level. (see details in ticket for what I tried out)

[sonarqubecloud]

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[loneil]

I suppose if anyone is using this dockerfile and counting on having the INFO level logs come out (even though they're not supposed to) they would be missing those after updating to a version including this fix. But in that case one should be setting their own deployment to INFO anyways...