MM-46874: Change to 400 for failed to upgrade ws (#21492)

https://mattermost.atlassian.net/browse/MM-46874

```release-note
NONE
```

api4/websocket.go

@@ -32,7 +32,7 @@ func connectWebSocket(c *Context, w http.ResponseWriter, r *http.Request) {
 
 	ws, err := upgrader.Upgrade(w, r, nil)
 	if err != nil {
-		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", nil, err.Error(), http.StatusInternalServerError)
+		c.Err = model.NewAppError("connect", "api.web_socket.connect.upgrade.app_error", nil, err.Error(), http.StatusBadRequest)
 		return
 	}