Refuse to listen to QT_PLUGIN_PATH.

We don't need it ourselves, and it's a potentially serious attack vector.

CURA-8475

cura_app.py

@@ -15,6 +15,7 @@ if "" in sys.path:
 import argparse
 import faulthandler
 import os
+os.environ["QT_PLUGIN_PATH"] = ""  # Security workaround: Don't need it, and introduces an attack vector, so set to nul.
 
 from PyQt5.QtNetwork import QSslConfiguration, QSslSocket