Fix a JET error around matching methods for read_worker_host_port(...) (#171)

```
┌ connect(manager::Distributed.SSHManager, pid::Int64, config::Distributed.WorkerConfig) @ Distributed /workpath/Distributed.jl/src/managers.jl:582
│ no matching method found `read_worker_host_port(::Nothing)` (1/2 union split): Distributed.read_worker_host_port((config::Distributed.WorkerConfig).io::Union{Nothing, IO})
└────────────────────
```

(cherry picked from commit d259b8d3cc24686430a7285abeed574ed46768e7)
(cherry picked from commit 0cf99106072adf5527acd48c668cd95c925e114f)

Author: DilumAluthge

src/managers.jl

@@ -606,7 +606,7 @@ function connect(manager::ClusterManager, pid::Int, config::WorkerConfig)
 
     # master connecting to workers
     if config.io !== nothing
-        (bind_addr, port::Int) = read_worker_host_port(config.io)
+        (bind_addr, port::Int) = read_worker_host_port(config.io::IO)
         pubhost = something(config.host, bind_addr)
         config.host = pubhost
         config.port = port