### Motivation
In the `HTTP1ConnectionStateMachine` we set the connection state to `.closed` after having forwarded an error to the inner RequestStateMachine. Since we set the state to close, the `state.modify` function did not create an action that would close the connection.
### Changes
- Modify the ConnectionState based on the RequestStateMachine's action only in the `state.modify` function.
- Add a test to verify the fixed behavior.
- Use ExpressibleByDictionaryLiteral syntax for some HTTPHeaders to increase readability.
### Result
Connections are closed, if an error happens, while we are in a request.
Fabian Fett
