Error setting a variable to an enum attribute

Describe the bug

Working on a serverless project in vscode, I came across this problem -
Trying to set a variable to an attribute defined as an enum - i get "value is not accepted. valid values: ...".

See this simplified version:

service: test-service

provider:
  name: aws
  region: ${env:AWS_REGION} # this value gets an error

Expected Behavior

I'd expect it to be a warning or less.

Current Behavior

I get an error reported.

Steps to Reproduce

Just put this example in a file called serverless.yml and open with vscode, then wait a bit for the linting to happen.
Adding useDotenv: true or using the serverless-dotenv-plugin doesn't change this.

Environment

• Windows
• Mac
• Linux
• other (please specify)

Reproduce the problem by opening the provided serverless.yml example in VS Code and waiting for linting. Investigate the YAML language server's handling of an environment-variable substitution in an enum-valued attribute; done means the substitution no longer produces an error, but is treated as a warning or less severe diagnostic.