Fix docker FROM AS/as warning.

[hjoliver]

After swarm build failed in CI (for other reasons - slow download?):

 135.6 critical libmamba Could not solve for environment specs
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 1 warning found (use docker --debug to expand):
 - FromAsCasing: 'as' and 'FROM' keywords' casing do not match (line 24)
Dockerfile:8
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(Does that really matter? 🤣 )

[oliver-sanders]

I think this is just lint, but whatever.

[hjoliver]

Yes it was just a warning (I said the build failed for other reasons).