Empty secret when set from environment variable with --secret id=MYSECRET,type=env

[r10r]

When playing with secrets I first passed with the following options:

MYSECRET=foobar buildah bud --secret id=MYSECRET,type=env

FROM alpine:latest
RUN --mount=type=secret,id=MYSECRET echo "MYSECRET: $(cat /run/secrets/MYSECRET)"

But the secret file is empty. Seems there is a missing case in https://github.com/containers/buildah/blob/release-1.37/pkg/parse/parse.go#L1264 that checks for type=env.

I know know after studying the code and the latest changes to the manual that I can simply omit thetype=env
but I still think that this case should be fixed.