Use certifi for firmware update checker

CURA-6698

plugins/FirmwareUpdateChecker/FirmwareUpdateCheckerJob.py

@@ -10,6 +10,9 @@ from UM.Version import Version
 import urllib.request
 from urllib.error import URLError
 from typing import Dict, Optional
+import ssl
+
+import certifi
 
 from .FirmwareUpdateCheckerLookup import FirmwareUpdateCheckerLookup, getSettingsKeyForMachine
 from .FirmwareUpdateCheckerMessage import FirmwareUpdateCheckerMessage
@@ -39,8 +42,12 @@ class FirmwareUpdateCheckerJob(Job):
         result = self.STRING_ZERO_VERSION
 
         try:
+            # CURA-6698 Create an SSL context and use certifi CA certificates for verification.
+            context = ssl.SSLContext(protocol = ssl.PROTOCOL_TLSv1_2)
+            context.load_verify_locations(cafile = certifi.where())
+
             request = urllib.request.Request(url, headers = self._headers)
-            response = urllib.request.urlopen(request)
+            response = urllib.request.urlopen(request, context = context)
             result = response.read().decode("utf-8")
         except URLError:
             Logger.log("w", "Could not reach '{0}', if this URL is old, consider removal.".format(url))