`GREENWOOD_VERSION` argument not being interpolated in Dockerfile

In the Dockerfile, for convenience, we have the version of Greenwood to be used as an ARG, just like NODE_VERSION

ARG GREENWOOD_VERSION=alpha

# ...

RUN npm i @greenwood/cli@${GREENWOOD_VERSION}

However, in our example above, in which we're using the alias alpha, we are actually just getting whatever is latest on npm (0.29.4) instead of the latest alpha (0.30.0-alpha.6)

[+] Running 1/0
 ✔ Container greenwood-demo-platform-docker-server-1  Created                                                              0.0s 
Attaching to server-1
server-1  | 
server-1  | > greenwood-demo-platform-docker@1.0.0 start
server-1  | > npm run serve
server-1  | 
server-1  | 
server-1  | > greenwood-demo-platform-docker@1.0.0 serve
server-1  | > greenwood serve
server-1  | 
server-1  | -------------------------------------------------------
server-1  | Welcome to Greenwood (v0.29.4) ♻️
server-1  | -------------------------------------------------------
server-1  | Initializing project config
server-1  | Initializing project workspace contexts
server-1  | Loading graph from build output...
server-1  | Loading manifest from build output...
server-1  | Loading resources from build output...
server-1  | Running Greenwood with the serve command.
server-1  | Started server at http://localhost:8080

It seems that per the logs, maybe it is not getting interpolated correctly? Maybe we just have the syntax wrong?

 => CACHED [server deps 2/2] RUN npm i @greenwood/cli@${GREENWOOD_VERSION}