Fix reference to HttpProxy after Qt6 change

After the switch to Qt6 (#156),
proxies were left broken due to a renaming in QNetworkProxy (which is
not properly documented in
https://doc.qt.io/qtforpython-6/PySide6/QtNetwork/QNetworkProxy.html#PySide6.QtNetwork.QNetworkProxy.ProxyType).

Rename to the enum scope to avoid a runtime error when trying to set
proxy.

kiosk/kiosk_browser/proxy.py

@@ -105,7 +105,7 @@ def find(f, xs):
 
 def set_proxy_in_qt_app(hostname, port):
     network_proxy = QNetworkProxy()
-    network_proxy.setType(QNetworkProxy.HttpProxy)
+    network_proxy.setType(QNetworkProxy.ProxyType.HttpProxy)
     network_proxy.setHostName(hostname)
     network_proxy.setPort(port)
     QNetworkProxy.setApplicationProxy(network_proxy)