"az ssh vm" does not go to the background

### Related command

```sh
az extension remove --name ssh && az extension add --name ssh --version 1.1.3

# Command does not go to the background
az ssh vm --hostname -- -f -N
> OpenSSH_8.6p1, LibreSSL 3.3.6

az extension remove --name ssh && az extension add --name ssh --version 1.1.2
# Command go to the background
az ssh vm --hostname -- -f -N
```

### Extension name (the extension in question)
ssh

### Description of issue (in as much detail as possible)

Prior to version 1.1.3 of the ssh extension, the command with the ssh flags `-f -N` went into the background. But with a newer version, the command stays in the foreground.