fix: handle SIGHUP from OpenSSH (#10638)

Fixes an issue where remote forwards are not correctly torn down when using OpenSSH with `coder ssh --stdio`.  OpenSSH sends a disconnect signal, but then also sends SIGHUP to `coder`.  Previously, we just exited when we got SIGHUP, and this raced against properly disconnecting.

Fixes https://github.com/coder/customers/issues/327

cli/externalauth.go

@@ -2,7 +2,6 @@ package cli
 
 import (
 	"encoding/json"
-	"os/signal"
 
 	"golang.org/x/xerrors"
 
@@ -63,7 +62,7 @@ fi
 		Handler: func(inv *clibase.Invocation) error {
 			ctx := inv.Context()
 
-			ctx, stop := signal.NotifyContext(ctx, InterruptSignals...)
+			ctx, stop := inv.SignalNotifyContext(ctx, InterruptSignals...)
 			defer stop()
 
 			client, err := r.createAgentClient()