actually enable warnings as errors (#759)
actually enable warnings as errors (#759)

Motivation:

Forgot to introduce the -warnings-as-errors parameter in the `test:`
directive in the docker compose file.

Modifications:

added warnings-to-errors to the docker-compose.yml for 5.0

Result:

warnings to errors
apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio,apple/swift-nio