Bug 1859819 - fix is_ubuntu to be accurate on windows xpcshell. r=gbrown

Differential Revision: https://phabricator.services.mozilla.com/D191326

testing/xpcshell/runxpcshelltests.py

@@ -8,6 +8,7 @@ import copy
 import json
 import os
 import pipes
+import platform
 import random
 import re
 import shutil
@@ -1564,6 +1565,8 @@ class XPCShellTests(object):
             "app_binary"
         ) is not None and "WindowsApps" in options.get("app_binary", "")
 
+        self.mozInfo["is_ubuntu"] = "Ubuntu" in platform.version()
+
         mozinfo.update(self.mozInfo)
 
         return True